enable outcropping of random JPG/PNG images

- Works best with runwayML inpainting model
- Numerous code changes required to propagate seed to final metadata.
  Original code predicated on the image being generated within InvokeAI.

ldm/generate.py

@@ -566,12 +566,13 @@ class Generate:
 
         args   = metadata_from_png(image_path)
         seed   = args.seed
-        prompt = args.prompt
-        print(f'>> retrieved seed {seed} and prompt "{prompt}" from {image_path}')
-
-        if not seed:
-            print('* Could not recover seed for image. Replacing with 42. This will not affect image quality')
-            seed = 42
+        prompt = args.prompt or ''
+        if seed == 0:
+            seed = random.randrange(0, np.iinfo(np.uint32).max)
+            opt.seed = seed
+            print(f'>> generated new seed {seed} and prompt "{prompt}" for {image_path}')
+        else:
+            print(f'>> retrieved seed {seed} and prompt "{prompt}" from {image_path}')
 
         # try to reuse the same filename prefix as the original file.
         # we take everything up to the first period