Fix fullscreen toggle bug

[wsldankers]

To reproduce:

1. Bind a key to toggle_fullscreen(2):

[keybindings]
<Escape> { toggle_fullscreen(2); }

2. Start pqiv with otherwise default options and keybindings, with a filename as argument

3. Press Escape

4. Press f (as often as you like)

Expected behavior: f in step 4 toggles fullscreen mode

Observed behavior: nothing happens.

Root cause:

a) The Escape in step 3 tries to leave fullscreen even when fullscreen is not active.

b) window_unfullscreen() then tries to set main_window_in_fullscreen to FALSE temporarily (even though it already was FALSE) then "restore" it incorrectly by setting it to TRUE.

c) This means main_window_in_fullscreen is now out of sync with reality.

d) From this point on, any attempt to toggle it will try to toggle it in the wrong direction.

Debug trace (pressed Escape once, then f twice):

pqiv.c:5748: action(): main_window_in_fullscreen=0 parameter.pint=2
pqiv.c:4191: window_unfullscreen(): main_window_in_fullscreen=0
pqiv.c:4230: window_unfullscreen(): main_window_in_fullscreen=1
pqiv.c:5748: action(): main_window_in_fullscreen=1 parameter.pint=0
pqiv.c:4191: window_unfullscreen(): main_window_in_fullscreen=1
pqiv.c:4230: window_unfullscreen(): main_window_in_fullscreen=1
pqiv.c:5748: action(): main_window_in_fullscreen=1 parameter.pint=0
pqiv.c:4191: window_unfullscreen(): main_window_in_fullscreen=1
pqiv.c:4230: window_unfullscreen(): main_window_in_fullscreen=1

[phillipberndt]

Oh, I thought I had posted a response already - sorry for taking long to actually do..

Thanks a lot for taking the time and already doing the debugging & finding a fix!

If you like, add a commit to add this change to the changelog in the readme, and yourself to the contributors list. Otherwise I'll merge this one of the next days & add an entry to the changelog myself.

[wsldankers]

Commit added!

[phillipberndt]

Thanks again! Merged.