Avoid `IndexError` when no face is detected

app.py

@@ -55,9 +55,11 @@ def generate_image(images, prompt, negative_prompt, preserve_face_structure, fac
     
     faceid_all_embeds = []
     first_iteration = True
-    for image in images:
+    for i, image in enumerate(images):
         face = cv2.imread(image)
         faces = app.get(face)
+        if len(faces) == 0:
+            raise gr.Error(f"No face detected in image number {i+1}")
         faceid_embed = torch.from_numpy(faces[0].normed_embedding).unsqueeze(0)
         faceid_all_embeds.append(faceid_embed)
         if(first_iteration and preserve_face_structure):