onExecutionFailure should be called before returning from run if backup is not valid

[serkan-ozal]

After this PR #6301, Backup operation can be read directly as object without reading it first as Data temporary.

However after the backup operation is read (deserialized) as object, if it is decided (at Backup::beforeRun so valid field is false) that current node is not backup of this replica anymore, Backup::run returns silently. But before it returns, it should call onExecutionFailure of the backup operation otherwise it causes native memory leaks due to undisposed native memory.