Fix exception from progress windows when comtypes isn't available.

Author: zewt

scripts/zMayaTools/taskbar_progress.py

@@ -48,6 +48,9 @@ class ProgressWindowWindowsTaskbarUnavailable(util.ProgressWindow):
         @classmethod
         def available(cls):
             return False
+
+        def set_total_progress_value(self, total_progress_values):
+            pass
 
     ProgressWindowWindowsTaskbar = ProgressWindowWindowsTaskbarUnavailable