SimEngineVEX: only use last_stmt when it is not None.
SimEngineVEX: only use last_stmt when it is not None.

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