Usage of -T with montage mode is overwritten

[Kwepoi]

If you want the window title to be a certain title, using 'pqiv -T foo' the title becomes foo correctly, but if you happen to spawn the window in montage mode with 'pqiv -T foo --browse --auto-montage-mode' the window will always only have the title "pqiv: Montage mode", the correct behavior should be that -T always allows what title the user assigns and if a title hasn't been assigned only then does it become "pqiv: Montage mode".

[phillipberndt]

Makes sense, and sounds like a simple miss that should be straightforward to fix. I'll be happy to take a PR here, I expect it'll be some time until I get around to this.