Empty vectors lead to segfaults

[TauIdMVATrainingNtupleProducerMiniAOD::tempSetValueVF](https://github.com/greyxray/TauAnalysisTools/commit/6723dd9e01f36fbbb8366c5ef638ef3a0b2eaa1f#diff-d78e0f19b54fa8a1682bf4154f53ee52R1373) method is a dirty hack to deal wit the events where the vectors remain empty.

commit: https://github.com/greyxray/TauAnalysisTools/commit/6723dd9e01f36fbbb8366c5ef638ef3a0b2eaa1f