bugfix: division by zero if only width or only height specified

setup.py

@@ -41,7 +41,7 @@ setuptools.setup(
     # For a discussion on single-sourcing the version across setup.py and the
     # project code, see
     # https://packaging.python.org/en/latest/single_source_version.html
-    version='18.1.4',  # Required
+    version='18.1.5',  # Required
 
     # This is a one-line description or tagline of what your project does. This
     # corresponds to the "Summary" metadata field:

ueberzug/loading.py

@@ -35,6 +35,9 @@ def load_image(path, upper_bound_size):
     mask = None
 
     if upper_bound_size:
+        upper_bound_size = tuple(
+            min(size for size in size_pair if size > 0)
+            for size_pair in zip(upper_bound_size, original_size))
         image.draft(None, upper_bound_size)
         downscaled = (image.width, image.height) < original_size