Fixes a problem that keeps the /web-page-replay-command-status command from working properly if the archive file is empty. 
Fixes a problem that keeps the /web-page-replay-command-status command from working properly if the archive file is empty. 

Patch contributed by: rmcloughlin@google.com

Issue=http://code.google.com/p/web-page-replay/issues/detail?id=28

git-svn-id: abd770af2affaf62930f25b244f6edafe8ddae5b@505 164481a5-15cb-f69f-4b93-856c5b7754c5

ting-yuan/web-page-replay,colin-scott/web-page-replay,colin-scott/web-page-replay,chromium/web-page-replay,andrey-malets/web-page-replay,snorp/web-page-replay,bpsinc-native/src_third_party_webpagereplay,chromium/web-page-replay,ting-yuan/web-page-replay,bpsinc-native/src_third_party_webpagereplay,snorp/web-page-replay,bpsinc-native/src_third_party_webpagereplay,andrey-malets/web-page-replay