Patch by Andi Albrecht to fix issue 18: diff of empty added file causes 500 error.
Patch by Andi Albrecht to fix issue 18: diff of empty added file causes
500 error.

fuzan/rietveld,nbodepallictr/touchites-test,aungzanbaw/rietveld,kscharding/integral-solutions-smxq,salomon1184/rietveld,rietveld-codereview/rietveld,salomon1184/rietveld,google-code-export/rietveld,nareshboddepalli/touchites-test,dushmis/rietveld,draem0507/rietveld,rietveld-codereview/rietveld,salomon1184/rietveld,Koulio/rietveld,robfig/rietveld,gavioto/rietveld,dushmis/rietveld,sajingeo/rietveld,andyzsf/rietveld,Koulio/rietveld,supriyantomaftuh/rietveld,aungzanbaw/rietveld,nareshboddepalli/touchites-codereview,draem0507/rietveld,v3ss0n/rietveld,berkus/rietveld,Koulio/rietveld,foolonhill/rietveld,sajingeo/rietveld,arg0/rietveld,openlabs/cr.openlabs.co.in,fuzan/rietveld,ericmckean/rietveld,nbodepallictr/touchites-test,google-code-export/rietveld,DeanHere/rietveld,gco/rietveld,nbodepallictr/touchites-codereview,v3ss0n/rietveld,DeanHere/rietveld,kscharding/integral-solutions-smxq,xtypebee/rietveld,arg0/rietveld,nbodepallictr/touchites-test,andyzsf/rietveld,xtypebee/rietveld,foolonhill/rietveld,robfig/rietveld,DeanHere/rietveld,robfig/rietveld,draem0507/rietveld,supriyantomaftuh/rietveld,rietveld-codereview/rietveld,foolonhill/rietveld,ericmckean/rietveld,google-code-export/rietveld,andyzsf/rietveld,nbodepallictr/touchites-codereview,arg0/rietveld,v3ss0n/rietveld,berkus/rietveld,nareshboddepalli/touchites-test,gavioto/rietveld,gavioto/rietveld,dushmis/rietveld,sajingeo/rietveld,nareshboddepalli/touchites-codereview,aungzanbaw/rietveld,supriyantomaftuh/rietveld,openlabs/cr.openlabs.co.in,nareshboddepalli/touchites-test,xtypebee/rietveld,kscharding/integral-solutions-smxq,gco/rietveld,rietveld-codereview/rietveld,gco/rietveld,ericmckean/rietveld,openlabs/cr.openlabs.co.in,fuzan/rietveld,nareshboddepalli/touchites-codereview,berkus/rietveld,nbodepallictr/touchites-codereview