add fix for output.wav not existing

app.py

@@ -20,6 +20,8 @@ def download_video(url):
 def split_audio(mindur, maxdur, name_for_split_files, show_amount_of_files_and_file_dur):
     if show_amount_of_files_and_file_dur == True:
         gr.Warning(f"show_amount_of_files_and_file_dur set to True. This feature may be inaccurate especially for WAV files, so dont rely too much on the count and duration.")
+    if not os.path.exists("output.wav"):
+        raise gr.Error("Output.wav does not exist! Did you do the first tab correctly or at all?")
     if mindur == maxdur:
         raise gr.Error(f"Cannot split mindur={mindur} and maxdur={maxdur}, min and max are the same number.")
     elif mindur > maxdur: