sanitizeRemoteFunctionException() can call JSValue::toWTFString() which may throw under certain circumstances.  However, it is only called here if exceptionValue.isPrimitive() i.e. it will never throw.  However, the exception check validator does not know this.  So, we added a `ASSERT(!scope.exception())` to placate it.  

However, if we're forcing exception check validation on a Release build, the ASSERT turns into a no-op.  The fix is to use EXCEPTION_ASSERT here instead.