overlay: prevent overlay from queueing up keyboard input while overlay is not visible (#677)

## Link to GitHub Issue or related Pull Request, if one exists
Fixes #675

Yet another regression from #604 

## Description of change
When overlay was hidden (not visible) it was still accepting keyboard
input, so when it became visible again the queued up keystrokes got
processed all at once.

Also, fix a bug with monitor settings update kicking in when in windowed
mode - this really should have been only for full screen.

## Testing
Tested DDR windowed / full screen, TDJ with subscreen overlay windowed /
fullscreen.

src/spice2x/hooks/graphics/graphics.cpp

@@ -1401,7 +1401,7 @@ void update_monitor_on_boot(std::optional<graphics_orientation> target_orientati
 }
 
 void update_monitor_at_runtime() {
-    if (monitor_settings_changed) {
+    if (!GRAPHICS_WINDOWED && monitor_settings_changed) {
         log_misc("graphics", "applying monitor updates at runtime as window regained focus...");
         update_monitor(false, target_orientation_on_boot, target_refresh_rate_on_boot);   
     }