ClassVerifier frees exception message while it's still in use

While testing the CompactStrings implementation, I encountered weird crashes in java_lang_String::create_from_str(const char* utf8_str) that were due to 'utf8_str' containing garbage.

V [libjvm.so+0x1160d00] VMError::report_and_die()+0x160
V [libjvm.so+0x83276f] report_should_not_reach_here(char const*, int)+0x6f
V [libjvm.so+0xae52df] java_lang_String::create_from_str(char const*, Thread*)+0x28f
V [libjvm.so+0x901ab5] Exceptions::new_exception(Thread*, Symbol*, char const*, Handle, Handle, Handle, Exceptions::ExceptionMsgToUtf8Mode)+0x225
V [libjvm.so+0x9021ab] Exceptions::_throw_msg(Thread*, char const*, int, Symbol*, char const*)+0x12b
V [libjvm.so+0x1142e5b] Verifier::verify(instanceKlassHandle, Verifier::Mode, bool, Thread*)+0xa9b

It turned out that the problem is in the ClassVerifier freeing the exception message while it's still in use.