mintUpdate.py: Fix auto-refresh loop race condition.

The refresh() function is an _idle function, and being called from
the auto-refresh thread. Because of this, the thread ends up looping
before the 'refresh-last-run' value can be updated, causing another
refresh to occur 1 minute later. This happens for every periodic
refresh.

ref: #1017

Author: mtwebster

usr/lib/linuxmint/mintUpdate/mintUpdate.py

@@ -1159,6 +1159,11 @@ def start_auto_refresh(self):
                     if self.hidden:
                         self.logger.write(f"Update Manager is in tray mode; performing {refresh_type} refresh")
                         self.refresh(True)
+                        # FIXME: self.refresh() is an _idle function, and we're on a thread - we will continue
+                        # and loop before self.refreshing is set. Force a brief dwell to allow the refresh() call
+                        # to get ahead of us and set self.refreshing and update 'refresh-last-run', otherwise we'll
+                        # get a double-refresh 1 minute apart every time.
+                        time.sleep(0.5)
                         while self.refreshing:
                             time.sleep(5)
                     else: