Fix read size 0 in shared ppb_file_io.
Fix read size 0 in shared ppb_file_io.

We check that the src and dst pointers are non-null, however a read of size
zero is a NOP.  Typically library behavior is to ignore invalid arguments when
no work is actually done.

BUG=110087
R=brettw@chromium.org

Review URL: http://codereview.chromium.org/9695021

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@126461 0039d316-1c4b-4281-b951-d872f2087c98

keishi/chromium,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,keishi/chromium,robclark/chromium,Fireblend/chromium-crosswalk,M4sse/chromium.src,rogerwang/chromium,littlstar/chromium.src,junmin-zhu/chromium-rivertrail,robclark/chromium,hgl888/chromium-crosswalk,nacl-webkit/chrome_deps,anirudhSK/chromium,hgl888/chromium-crosswalk-efl,hgl888/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,pozdnyakov/chromium-crosswalk,M4sse/chromium.src,axinging/chromium-crosswalk,robclark/chromium,nacl-webkit/chrome_deps,hgl888/chromium-crosswalk-efl,robclark/chromium,pozdnyakov/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,keishi/chromium,anirudhSK/chromium,bright-sparks/chromium-spacewalk,krieger-od/nwjs_chromium.src,fujunwei/chromium-crosswalk,Chilledheart/chromium,keishi/chromium,Just-D/chromium-1,mohamed--abdel-maksoud/chromium.src,rogerwang/chromium,hujiajie/pa-chromium,ondra-novak/chromium.src,robclark/chromium,dednal/chromium.src,dushu1203/chromium.src,hgl888/chromium-crosswalk-efl,timopulkkinen/BubbleFish,patrickm/chromium.src,Pluto-tv/chromium-crosswalk,dednal/chromium.src,markYoungH/chromium.src,zcbenz/cefode-chromium,dushu1203/chromium.src,fujunwei/chromium-crosswalk,bright-sparks/chromium-spacewalk,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Fireblend/chromium-crosswalk,junmin-zhu/chromium-rivertrail,rogerwang/chromium,timopulkkinen/BubbleFish,hgl888/chromium-crosswalk-efl,ChromiumWebApps/chromium,ondra-novak/chromium.src,TheTypoMaster/chromium-crosswalk,pozdnyakov/chromium-crosswalk,patrickm/chromium.src,anirudhSK/chromium,nacl-webkit/chrome_deps,mogoweb/chromium-crosswalk,hujiajie/pa-chromium,hujiajie/pa-chromium,dushu1203/chromium.src,ondra-novak/chromium.src,pozdnyakov/chromium-crosswalk,junmin-zhu/chromium-rivertrail,zcbenz/cefode-chromium,mohamed--abdel-maksoud/chromium.src,keishi/chromium,anirudhSK/chromium,rogerwang/chromium,Jonekee/chromium.src,M4sse/chromium.src,crosswalk-project/chromium-crosswalk-efl,ChromiumWebApps/chromium,keishi/chromium,pozdnyakov/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,hujiajie/pa-chromium,bright-sparks/chromium-spacewalk,ltilve/chromium,dushu1203/chromium.src,PeterWangIntel/chromium-crosswalk,hgl888/chromium-crosswalk,mogoweb/chromium-crosswalk,fujunwei/chromium-crosswalk,jaruba/chromium.src,timopulkkinen/BubbleFish,keishi/chromium,mohamed--abdel-maksoud/chromium.src,Jonekee/chromium.src,anirudhSK/chromium,markYoungH/chromium.src,markYoungH/chromium.src,nacl-webkit/chrome_deps,axinging/chromium-crosswalk,patrickm/chromium.src,dednal/chromium.src,Chilledheart/chromium,ChromiumWebApps/chromium,bright-sparks/chromium-spacewalk,mohamed--abdel-maksoud/chromium.src,TheTypoMaster/chromium-crosswalk,dednal/chromium.src,ltilve/chromium,rogerwang/chromium,nacl-webkit/chrome_deps,zcbenz/cefode-chromium,Fireblend/chromium-crosswalk,dushu1203/chromium.src,rogerwang/chromium,ondra-novak/chromium.src,markYoungH/chromium.src,hujiajie/pa-chromium,crosswalk-project/chromium-crosswalk-efl,patrickm/chromium.src,ondra-novak/chromium.src,ondra-novak/chromium.src,markYoungH/chromium.src,PeterWangIntel/chromium-crosswalk,fujunwei/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,nacl-webkit/chrome_deps,axinging/chromium-crosswalk,Jonekee/chromium.src,hgl888/chromium-crosswalk-efl,junmin-zhu/chromium-rivertrail,robclark/chromium,patrickm/chromium.src,M4sse/chromium.src,robclark/chromium,crosswalk-project/chromium-crosswalk-efl,markYoungH/chromium.src,pozdnyakov/chromium-crosswalk,timopulkkinen/BubbleFish,nacl-webkit/chrome_deps,crosswalk-project/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,keishi/chromium,Jonekee/chromium.src,junmin-zhu/chromium-rivertrail,Just-D/chromium-1,axinging/chromium-crosswalk,krieger-od/nwjs_chromium.src,keishi/chromium,PeterWangIntel/chromium-crosswalk,dushu1203/chromium.src,hgl888/chromium-crosswalk-efl,nacl-webkit/chrome_deps,bright-sparks/chromium-spacewalk,TheTypoMaster/chromium-crosswalk,Jonekee/chromium.src,fujunwei/chromium-crosswalk,hgl888/chromium-crosswalk-efl,ltilve/chromium,mogoweb/chromium-crosswalk,bright-sparks/chromium-spacewalk,robclark/chromium,ChromiumWebApps/chromium,ltilve/chromium,M4sse/chromium.src,keishi/chromium,hgl888/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,mohamed--abdel-maksoud/chromium.src,Chilledheart/chromium,mohamed--abdel-maksoud/chromium.src,crosswalk-project/chromium-crosswalk-efl,ltilve/chromium,pozdnyakov/chromium-crosswalk,dednal/chromium.src,littlstar/chromium.src,jaruba/chromium.src,Just-D/chromium-1,pozdnyakov/chromium-crosswalk,M4sse/chromium.src,Fireblend/chromium-crosswalk,littlstar/chromium.src,mohamed--abdel-maksoud/chromium.src,krieger-od/nwjs_chromium.src,keishi/chromium,ChromiumWebApps/chromium,bright-sparks/chromium-spacewalk,hujiajie/pa-chromium,axinging/chromium-crosswalk,ondra-novak/chromium.src,pozdnyakov/chromium-crosswalk,jaruba/chromium.src,ltilve/chromium,hgl888/chromium-crosswalk-efl,anirudhSK/chromium,bright-sparks/chromium-spacewalk,chuan9/chromium-crosswalk,mogoweb/chromium-crosswalk,anirudhSK/chromium,PeterWangIntel/chromium-crosswalk,mogoweb/chromium-crosswalk,chuan9/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,junmin-zhu/chromium-rivertrail,timopulkkinen/BubbleFish,hujiajie/pa-chromium,Pluto-tv/chromium-crosswalk,patrickm/chromium.src,jaruba/chromium.src,fujunwei/chromium-crosswalk,junmin-zhu/chromium-rivertrail,junmin-zhu/chromium-rivertrail,mogoweb/chromium-crosswalk,timopulkkinen/BubbleFish,dednal/chromium.src,fujunwei/chromium-crosswalk,axinging/chromium-crosswalk,markYoungH/chromium.src,ondra-novak/chromium.src,M4sse/chromium.src,littlstar/chromium.src,dednal/chromium.src,hujiajie/pa-chromium,rogerwang/chromium,ChromiumWebApps/chromium,Pluto-tv/chromium-crosswalk,zcbenz/cefode-chromium,patrickm/chromium.src,pozdnyakov/chromium-crosswalk,Jonekee/chromium.src,mogoweb/chromium-crosswalk,Just-D/chromium-1,dednal/chromium.src,anirudhSK/chromium,Fireblend/chromium-crosswalk,junmin-zhu/chromium-rivertrail,Pluto-tv/chromium-crosswalk,zcbenz/cefode-chromium,PeterWangIntel/chromium-crosswalk,dednal/chromium.src,axinging/chromium-crosswalk,chuan9/chromium-crosswalk,ChromiumWebApps/chromium,littlstar/chromium.src,nacl-webkit/chrome_deps,TheTypoMaster/chromium-crosswalk,dushu1203/chromium.src,nacl-webkit/chrome_deps,bright-sparks/chromium-spacewalk,dednal/chromium.src,hgl888/chromium-crosswalk,chuan9/chromium-crosswalk,Chilledheart/chromium,hujiajie/pa-chromium,jaruba/chromium.src,Chilledheart/chromium,markYoungH/chromium.src,zcbenz/cefode-chromium,ChromiumWebApps/chromium,Fireblend/chromium-crosswalk,markYoungH/chromium.src,Pluto-tv/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk-efl,crosswalk-project/chromium-crosswalk-efl,Fireblend/chromium-crosswalk,fujunwei/chromium-crosswalk,Jonekee/chromium.src,M4sse/chromium.src,PeterWangIntel/chromium-crosswalk,dushu1203/chromium.src,anirudhSK/chromium,Just-D/chromium-1,jaruba/chromium.src,markYoungH/chromium.src,anirudhSK/chromium,timopulkkinen/BubbleFish,Chilledheart/chromium,zcbenz/cefode-chromium,ltilve/chromium,Chilledheart/chromium,mogoweb/chromium-crosswalk,M4sse/chromium.src,Chilledheart/chromium,M4sse/chromium.src,jaruba/chromium.src,Jonekee/chromium.src,hgl888/chromium-crosswalk,ChromiumWebApps/chromium,patrickm/chromium.src,dushu1203/chromium.src,zcbenz/cefode-chromium,ChromiumWebApps/chromium,littlstar/chromium.src,robclark/chromium,hujiajie/pa-chromium,hgl888/chromium-crosswalk-efl,Just-D/chromium-1,krieger-od/nwjs_chromium.src,crosswalk-project/chromium-crosswalk-efl,Pluto-tv/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,jaruba/chromium.src,chuan9/chromium-crosswalk,fujunwei/chromium-crosswalk,littlstar/chromium.src,M4sse/chromium.src,zcbenz/cefode-chromium,krieger-od/nwjs_chromium.src,Just-D/chromium-1,chuan9/chromium-crosswalk,zcbenz/cefode-chromium,mogoweb/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,krieger-od/nwjs_chromium.src,PeterWangIntel/chromium-crosswalk,axinging/chromium-crosswalk,timopulkkinen/BubbleFish,hujiajie/pa-chromium,Just-D/chromium-1,dushu1203/chromium.src,timopulkkinen/BubbleFish,timopulkkinen/BubbleFish,Fireblend/chromium-crosswalk,ondra-novak/chromium.src,rogerwang/chromium,timopulkkinen/BubbleFish,jaruba/chromium.src,ChromiumWebApps/chromium,Jonekee/chromium.src,patrickm/chromium.src,hgl888/chromium-crosswalk,junmin-zhu/chromium-rivertrail,rogerwang/chromium,TheTypoMaster/chromium-crosswalk,Pluto-tv/chromium-crosswalk,hgl888/chromium-crosswalk,ltilve/chromium,Just-D/chromium-1,rogerwang/chromium,anirudhSK/chromium,chuan9/chromium-crosswalk,anirudhSK/chromium,chuan9/chromium-crosswalk,junmin-zhu/chromium-rivertrail,mohamed--abdel-maksoud/chromium.src,dednal/chromium.src,krieger-od/nwjs_chromium.src,hgl888/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,krieger-od/nwjs_chromium.src,dushu1203/chromium.src,mogoweb/chromium-crosswalk,Jonekee/chromium.src,krieger-od/nwjs_chromium.src,Fireblend/chromium-crosswalk,axinging/chromium-crosswalk,nacl-webkit/chrome_deps,markYoungH/chromium.src,chuan9/chromium-crosswalk,jaruba/chromium.src,jaruba/chromium.src,ChromiumWebApps/chromium,ltilve/chromium,littlstar/chromium.src,zcbenz/cefode-chromium,pozdnyakov/chromium-crosswalk,krieger-od/nwjs_chromium.src,robclark/chromium,Jonekee/chromium.src