avoid running timers after collection unload

fixes:
- onRefreshTimer() firing when collection is in the process of
unloading
- saveNow() in the no changes case, which fires a timer 10ms later

aqt/main.py

@@ -62,7 +62,7 @@ class AnkiQt(QMainWindow):
             self.onAppMsg(args[0])
         # Load profile in a timer so we can let the window finish init and not
         # close on profile load error.
-        self.progress.timer(10, self.setupProfile, False)
+        self.progress.timer(10, self.setupProfile, False, requiresCollection=False)
 
     def setupUI(self):
         self.col = None
@@ -1311,7 +1311,7 @@ Please ensure a profile is open and Anki is not busy, then try again."""),
 
     def gcWindow(self, obj):
         obj.deleteLater()
-        self.progress.timer(1000, self.doGC, False)
+        self.progress.timer(1000, self.doGC, False, requiresCollection=False)
 
     def disableGC(self):
         gc.collect()

aqt/progress.py

@@ -58,11 +58,15 @@ class ProgressManager:
     # automatically defers until the DB is not busy, and avoids running
     # while a progress window is visible.
 
-    def timer(self, ms, func, repeat):
+    def timer(self, ms, func, repeat, requiresCollection=True):
         def handler():
             if self.inDB or self._levels:
                 # retry in 100ms
-                self.timer(100, func, False)
+                self.timer(100, func, False, requiresCollection)
+            elif not self.mw.col and requiresCollection:
+                # ignore timer events that fire after collection has been
+                # unloaded
+                print("Ignored progress func as collection unloaded: %s" % repr(func))
             else:
                 func()
         t = QTimer(self.mw)