fix(rendering): prevent index error on empty midi processing

The `Render_MIDI` function would crash with an `IndexError` if it received a MIDI with no notes, typically from a failed transcription.

app.py

@@ -633,10 +633,21 @@ def Render_MIDI(input_midi_path,
     # --- MIDI Processing using TMIDIX ---
     print('Processing MIDI... Please wait...')
     raw_score = MIDI.midi2single_track_ms_score(fdata)
-    escore = TMIDIX.advanced_score_processor(raw_score, 
-                                             return_enhanced_score_notes=True, 
-                                             apply_sustain=render_with_sustains
-                                            )[0]
+    # call the function and store the returned list in a variable.
+    processed_scores = TMIDIX.advanced_score_processor(raw_score, 
+                                                   return_enhanced_score_notes=True, 
+                                                   apply_sustain=render_with_sustains)
+    # check if the returned list is empty. This happens when transcription finds no notes.
+    # This check prevents the 'IndexError: list index out of range'.
+    if not processed_scores:
+        # If it is empty, print a warning and return a user-friendly error message.
+        print("Warning: MIDI file contains no processable notes.")
+        # The number of returned values must match the function's expected output.
+        # We return a tuple with empty or placeholder values for all 7 output components.
+        return ("N/A", fn1, "MIDI file contains no notes.", None, None, None, "No notes found.")
+
+    # If the list is not empty, it is now safe to get the first element.
+    escore = processed_scores[0]
 
     # Handle cases where the MIDI might not contain any notes
     if not escore: