Crash in test_IndexedInterceptorWithGetOwnPropertyDescriptor

[sdwilsh]

Similar to #83:

test_api.exe!v8::Value::IsString()  Line 501 + 0xa bytes    C++
test_api.exe!ExpectString(const char * code=0x00487fac, const char * expected=0x00487fe8)  Line 111 + 0x1e bytes    C++
test_api.exe!test_IndexedInterceptorWithGetOwnPropertyDescriptor()  Line 1895 + 0xe bytes   C++
test_api.exe!main(int aArgc=0x00000001, char * * aArgv=0x00955af8)  Line 60 + 0x7 bytes C++

We end up throwing an exception, which results in an empty Handle.