Initialize value.

[zahiraam]

This is an error detected by a static analyzer.

[tahonermann]

The static analysis tool produced a false positive; I see no reason for a change. The static analyzer failed to recognize that APValue::Kind is initialized to None during default construction of the EvalResult variable and that it can't have changed by the time the variable is destructed. The static analyzer falsely determined that DestroyDataAndMakeUninit() could be called from the APValue destructor.