Avoid progress window pop-up when application not focused

A 10ms delay was chosen as it tends to result in the progress window
appearing immediately when clicking into the unfocused window, preventing
another action from being started before the progress window appears.

Closes #1873

qt/aqt/progress.py

@@ -287,6 +287,11 @@ class ProgressManager:
         return self._levels
 
     def _on_show_timer(self) -> None:
+        if self.mw.app.focusWindow() is None:
+            # if no window is focused (eg app is minimized), defer display
+            self._show_timer.start(10)
+            return
+
         self._show_timer = None
         self._showWin()