CFGFast: Fix a crash in removing fake ret edges.
CFGFast: Fix a crash in removing fake ret edges.

f-prettyland/angr,iamahuman/angr,f-prettyland/angr,angr/angr,tyb0807/angr,axt/angr,angr/angr,schieb/angr,iamahuman/angr,iamahuman/angr,angr/angr,schieb/angr,chubbymaggie/angr,schieb/angr,axt/angr,tyb0807/angr,f-prettyland/angr,chubbymaggie/angr,chubbymaggie/angr,axt/angr,tyb0807/angr