fix #49: generating a default value instead of a symbolic variable when accessing non-existant memory addresses in non-symbolic mode
fix #49: generating a default value instead of a symbolic variable when accessing non-existant memory addresses in non-symbolic mode

chubbymaggie/angr,chubbymaggie/angr,tyb0807/angr,chubbymaggie/simuvex,schieb/angr,schieb/angr,angr/angr,iamahuman/angr,chubbymaggie/angr,angr/angr,tyb0807/angr,zhuyue1314/simuvex,tyb0807/angr,f-prettyland/angr,axt/angr,iamahuman/angr,angr/simuvex,axt/angr,f-prettyland/angr,chubbymaggie/simuvex,axt/angr,chubbymaggie/simuvex,angr/angr,schieb/angr,f-prettyland/angr,iamahuman/angr