mintUpdate.py: Fix hidden state tracking.

Initializing self.hidden to False was causing periodic refreshes
to be skipped, if the user never opened the window.

Fixes #923.
ref: https://forums.linuxmint.com/viewtopic.php?p=2590027#p2590027

usr/lib/linuxmint/mintUpdate/mintUpdate.py

@@ -182,7 +182,7 @@ def __init__(self):
         self.refreshing_flatpak = False
         self.refreshing_cinnamon = False
         self.auto_refresh_is_alive = False
-        self.hidden = False # whether the window is hidden or not
+        self.hidden = True # whether the window is hidden or not
         self.packages = [] # packages selected for update
         self.flatpaks = [] # flatpaks selected for update
         self.spices = [] # spices selected for update
@@ -507,7 +507,7 @@ def __init__(self):
             if len(sys.argv) > 1:
                 showWindow = sys.argv[1]
                 if showWindow == "show":
-                    self.ui_window.present_with_time(Gtk.get_current_event_time())
+                    self.show_window()
 
             if CINNAMON_SUPPORT:
                 self.cinnamon_updater = cinnamon.UpdateManager()