Change grid row count autodetect to prevent empty spots

Instead of just rounding (sometimes resulting in grids with "empty" spots), find a divisor.
For example: 8 images will now result in a 4x2 grid instead of a 3x3 with one empty spot.

modules/images.py

@@ -25,8 +25,9 @@ def image_grid(imgs, batch_size=1, rows=None):
         elif opts.n_rows == 0:
             rows = batch_size
         else:
-            rows = math.sqrt(len(imgs))
-            rows = round(rows)
+            rows = math.floor(math.sqrt(len(imgs)))
+            while len(imgs) % rows != 0:
+                rows -= 1
 
     cols = math.ceil(len(imgs) / rows)