Clean up blob diff path
Clean up blob diff path

Previously when diffing blobs, the diff code just ran with a NULL
repository object. Of course, that's not necessary and the test
for a NULL repo was confusing. This makes the blob diff run with
the repo that contains the blobs and clarifies the test that it
is possible to be diffing data where the path is unknown.

rcorre/libgit2,jamieleecool/ptest,dleehr/libgit2,zodiac/libgit2.js,joshtriplett/libgit2,Aorjoa/libgit2_maked_lib,spraints/libgit2,Corillian/libgit2,ardumont/libgit2,t0xicCode/libgit2,whoisj/libgit2,Snazz2001/libgit2,skabel/manguse,Tousiph/Demo1,mhp/libgit2,since2014/libgit2,t0xicCode/libgit2,mcanthony/libgit2,rcorre/libgit2,kissthink/libgit2,joshtriplett/libgit2,ardumont/libgit2,mhp/libgit2,MrHacky/libgit2,swisspol/DEMO-libgit2,Corillian/libgit2,yosefhackmon/libgit2,chiayolin/libgit2,JIghtuse/libgit2,yongthecoder/libgit2,yosefhackmon/libgit2,raybrad/libit2,oaastest/libgit2,mcanthony/libgit2,joshtriplett/libgit2,Corillian/libgit2,joshtriplett/libgit2,stewid/libgit2,Tousiph/Demo1,saurabhsuniljain/libgit2,saurabhsuniljain/libgit2,stewid/libgit2,maxiaoqian/libgit2,sim0629/libgit2,linquize/libgit2,evhan/libgit2,iankronquist/libgit2,Aorjoa/libgit2_maked_lib,yongthecoder/libgit2,maxiaoqian/libgit2,mingyaaaa/libgit2,Snazz2001/libgit2,Corillian/libgit2,jeffhostetler/public_libgit2,kenprice/libgit2,raybrad/libit2,sim0629/libgit2,dleehr/libgit2,spraints/libgit2,whoisj/libgit2,JIghtuse/libgit2,jflesch/libgit2-mariadb,mhp/libgit2,leoyanggit/libgit2,JIghtuse/libgit2,linquize/libgit2,since2014/libgit2,jamieleecool/ptest,ardumont/libgit2,mhp/libgit2,oaastest/libgit2,whoisj/libgit2,nokiddin/libgit2,since2014/libgit2,Tousiph/Demo1,kissthink/libgit2,KTXSoftware/libgit2,whoisj/libgit2,falqas/libgit2,spraints/libgit2,spraints/libgit2,Aorjoa/libgit2_maked_lib,nokiddin/libgit2,MrHacky/libgit2,sygool/libgit2,zodiac/libgit2.js,magnus98/TEST,amyvmiwei/libgit2,mhp/libgit2,dleehr/libgit2,Tousiph/Demo1,since2014/libgit2,leoyanggit/libgit2,oaastest/libgit2,oaastest/libgit2,kenprice/libgit2,skabel/manguse,falqas/libgit2,evhan/libgit2,stewid/libgit2,iankronquist/libgit2,whoisj/libgit2,kenprice/libgit2,chiayolin/libgit2,amyvmiwei/libgit2,nacho/libgit2,t0xicCode/libgit2,kissthink/libgit2,Aorjoa/libgit2_maked_lib,chiayolin/libgit2,sim0629/libgit2,Snazz2001/libgit2,evhan/libgit2,zodiac/libgit2.js,stewid/libgit2,nokiddin/libgit2,jamieleecool/ptest,raybrad/libit2,nacho/libgit2,falqas/libgit2,mrksrm/Mingijura,jeffhostetler/public_libgit2,zodiac/libgit2.js,t0xicCode/libgit2,jflesch/libgit2-mariadb,magnus98/TEST,swisspol/DEMO-libgit2,yosefhackmon/libgit2,jflesch/libgit2-mariadb,yongthecoder/libgit2,KTXSoftware/libgit2,rcorre/libgit2,leoyanggit/libgit2,dleehr/libgit2,ardumont/libgit2,oaastest/libgit2,kenprice/libgit2,amyvmiwei/libgit2,KTXSoftware/libgit2,iankronquist/libgit2,ardumont/libgit2,jflesch/libgit2-mariadb,yongthecoder/libgit2,jflesch/libgit2-mariadb,nacho/libgit2,magnus98/TEST,MrHacky/libgit2,mrksrm/Mingijura,claudelee/libgit2,saurabhsuniljain/libgit2,t0xicCode/libgit2,maxiaoqian/libgit2,skabel/manguse,amyvmiwei/libgit2,JIghtuse/libgit2,rcorre/libgit2,linquize/libgit2,t0xicCode/libgit2,joshtriplett/libgit2,jeffhostetler/public_libgit2,raybrad/libit2,yosefhackmon/libgit2,sygool/libgit2,spraints/libgit2,rcorre/libgit2,swisspol/DEMO-libgit2,kenprice/libgit2,Snazz2001/libgit2,Tousiph/Demo1,sim0629/libgit2,sygool/libgit2,magnus98/TEST,mrksrm/Mingijura,mrksrm/Mingijura,chiayolin/libgit2,skabel/manguse,yosefhackmon/libgit2,nokiddin/libgit2,spraints/libgit2,saurabhsuniljain/libgit2,stewid/libgit2,mingyaaaa/libgit2,skabel/manguse,sim0629/libgit2,kissthink/libgit2,mrksrm/Mingijura,claudelee/libgit2,Snazz2001/libgit2,maxiaoqian/libgit2,jeffhostetler/public_libgit2,yongthecoder/libgit2,KTXSoftware/libgit2,saurabhsuniljain/libgit2,ardumont/libgit2,kissthink/libgit2,whoisj/libgit2,falqas/libgit2,chiayolin/libgit2,Tousiph/Demo1,MrHacky/libgit2,jeffhostetler/public_libgit2,Corillian/libgit2,nacho/libgit2,sygool/libgit2,sygool/libgit2,JIghtuse/libgit2,leoyanggit/libgit2,jamieleecool/ptest,linquize/libgit2,maxiaoqian/libgit2,JIghtuse/libgit2,nokiddin/libgit2,kissthink/libgit2,kenprice/libgit2,since2014/libgit2,KTXSoftware/libgit2,falqas/libgit2,claudelee/libgit2,mcanthony/libgit2,mcanthony/libgit2,claudelee/libgit2,MrHacky/libgit2,sygool/libgit2,falqas/libgit2,raybrad/libit2,claudelee/libgit2,mingyaaaa/libgit2,mcanthony/libgit2,linquize/libgit2,sim0629/libgit2,amyvmiwei/libgit2,zodiac/libgit2.js,chiayolin/libgit2,dleehr/libgit2,dleehr/libgit2,mhp/libgit2,yongthecoder/libgit2,iankronquist/libgit2,leoyanggit/libgit2,iankronquist/libgit2,rcorre/libgit2,oaastest/libgit2,swisspol/DEMO-libgit2,claudelee/libgit2,evhan/libgit2,swisspol/DEMO-libgit2,mingyaaaa/libgit2,KTXSoftware/libgit2,jeffhostetler/public_libgit2,jflesch/libgit2-mariadb,mingyaaaa/libgit2,mcanthony/libgit2,magnus98/TEST,joshtriplett/libgit2,yosefhackmon/libgit2,stewid/libgit2,magnus98/TEST,skabel/manguse,Corillian/libgit2,saurabhsuniljain/libgit2,leoyanggit/libgit2,nokiddin/libgit2,Aorjoa/libgit2_maked_lib,maxiaoqian/libgit2,mingyaaaa/libgit2,MrHacky/libgit2,since2014/libgit2,linquize/libgit2,swisspol/DEMO-libgit2,amyvmiwei/libgit2,iankronquist/libgit2,Snazz2001/libgit2,mrksrm/Mingijura