Fix prompt matrix #rows/#cols when using hires

- images.draw_prompt_matrix() should be called with the final width/height
  of the generated images, after upscaling.
  Otherwise, the number of rows/cols computed in images.draw_grid_annotations
  will increase by the upscaling factor.
- Round the number of cols/rows in images.draw_grid_annotations, since
  the final images width may be a bit less than the required
  hr_upscale_to_x/y

modules/images.py

@@ -171,8 +171,8 @@ def draw_grid_annotations(im, width, height, hor_texts, ver_texts):
 
     pad_left = 0 if sum([sum([len(line.text) for line in lines]) for lines in ver_texts]) == 0 else width * 3 // 4
 
-    cols = im.width // width
-    rows = im.height // height
+    cols = round(im.width / width)
+    rows = round(im.height / height)
 
     assert cols == len(hor_texts), f'bad number of horizontal texts: {len(hor_texts)}; must be {cols}'
     assert rows == len(ver_texts), f'bad number of vertical texts: {len(ver_texts)}; must be {rows}'