Fixed bug when playing ads over 30 seconds

Because there is no way to get the length of an ad, the app just assumes every ad 30 seconds long.
This would cause a crash when an ad over 30 seconds would play.

src/gui.py

@@ -269,8 +269,8 @@ def __init__(self, *args, **kwargs):
         self.length_lbl.pack(side=LEFT, padx=8)
 
     def update_progress(self, progress:timedelta, length:timedelta):
-        progress_seconds = progress.total_seconds()
         length_seconds = length.total_seconds()
+        progress_seconds = min(progress.total_seconds(), length_seconds)
 
         value = (progress_seconds/length_seconds)*100
         self.progress_bar.config(value=value)