Fix validation in StoreVolumeFileLabel

[mzur]

core/app/Http/Requests/StoreVolumeFileLabel.php

Line 33 in 037e7dc

$this->label = Label::find($this->input('label_id'));

The label_id is used before it is validated in the form request. Since the label is required for authorization, we have to add a manual check if the value is an integer here.

Without validation, invalid input (e.g. a string) can produce a server error.