x11: fix keyboard input with control modifier active

[falkTX]

In X11, using Ubuntu 22.04 KDE Plasma desktop, I could not get proper keyboard events while the control key was held down.

I added a print right after the x11 utf8 key decode, like so:

  printf("x11 special:%d ufound:%d key:%d:'%c' %02x:%02x:'%s'\n",
           special, ufound, event->key.key, event->key.key, ustr[0], ustr[1], ustr);

And this was the print out for Ctrl+C:

x11 special:0 ufound:1 key:3:'' 03:00:''

After the fix from this PR, the following is printed, and yes it then works as expected:

x11 special:0 ufound:1 key:99:'c' 63:00:'c'

[drobilla]

This fixes (arguably, I guess) the key, but there's still text entry of a control character.

[drobilla]

On X11, that's just what the lookup stuff does. I don't know if all such events should just be filtered, or if this breaks whatever input method, or...

[falkTX]

I checked with other modifiers, Alt and Meta still get the key properly, only Control modifier made it lose the regular keys.

[drobilla]

Yeah, it's because the control key is a set bit, at least, uh "traditionally". In this case, I guess they should "always" (?) be filtered out, and it seems weird that the X string lookup stuff does this, but whatever I guess, that's a separate issue. Seems obvious the PuglKeyPressEvent::key shouldn't be shifted/"controlled" here regardless.

Merged as a7803c9, thanks.