Changed DTAttributedTextContentView to discard invalid CGContexts.
Changed DTAttributedTextContentView to discard invalid CGContexts.

Cocoanetics/DTCoreText,wangmb/DTCoreText,yaoxiaoyong/DTCoreText,appunite/DTCoreText,liulinjian/DTCoreText,rain1988/DTCoreText,rgregg/DTCoreText,appunite/DTCoreText,z8927623/DTCoreText,SanjoDeundiak/DTCoreText,AmberWhiteSky/DTCoreText,shuoshi/DTCoreText,niklassaers/DTCoreText,devontech/DTCoreText,openresearch/DTCoreText,z8927623/DTCoreText,sujeking/DTCoreText,1yvT0s/DTCoreText,xiaoyanit/DTCoreText,CoderJWYang/DTCoreText,shuoshi/DTCoreText,canyu9512/DTCoreText,cnbin/DTCoreText,SanjoDeundiak/DTCoreText,thusfresh/DTCoreText,cnbin/DTCoreText,davbeck/DTCoreText,qskycolor/DTCoreText,canyu9512/DTCoreText,rain1988/DTCoreText,wangmb/DTCoreText,pivotaltracker/DTCoreText,gank0326/CoreTextWithHTML,Akylas/DTCoreText,liulinjian/DTCoreText,niklassaers/DTCoreText,i-miss-you/DTCoreText,youprofit/DTCoreText,jingchunYuan/DTCoreText,Akylas/DTCoreText,rgregg/DTCoreText,Esdeath/DTCoreText,Cocoanetics/DTCoreText,thusfresh/DTCoreText,1yvT0s/DTCoreText,liuslevis/DTCoreText,goodheart/DTCoreText,davbeck/DTCoreText,jingchunYuan/DTCoreText,goodheart/DTCoreText,gank0326/CoreTextWithHTML,qskycolor/DTCoreText,Cocoanetics/DTCoreText,AmberWhiteSky/DTCoreText,sujeking/DTCoreText,w2592583/DTCoreText,iwakevin/DTCoreText,i-miss-you/DTCoreText,gnr/DTCoreText,programming086/DTCoreText,devontech/DTCoreText,iwakevin/DTCoreText