fix in s_variable so we allow SimRegisterVariable.reg to be None (it happens for GetI)
fix in s_variable so we allow SimRegisterVariable.reg to be None (it happens for GetI)

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