Fix unexpected error when saving image with zero dimension

Author: radarhere

Tests/test_file_gif.py

@@ -310,6 +310,14 @@ def test_roundtrip_save_all_1(tmp_path: Path) -> None:
         assert reloaded.getpixel((0, 0)) == 255
 
 
+@pytest.mark.parametrize("size", ((0, 1), (1, 0), (0, 0)))
+def test_save_zero(size: tuple[int, int]) -> None:
+    b = BytesIO()
+    im = Image.new("RGB", size)
+    with pytest.raises(SystemError):
+        im.save(b, "GIF")
+
+
 @pytest.mark.parametrize(
     "path, mode",
     (

src/PIL/GifImagePlugin.py

@@ -937,7 +937,13 @@ def _get_optimize(im: Image.Image, info: dict[str, Any]) -> list[int] | None:
     :param info: encoderinfo
     :returns: list of indexes of palette entries in use, or None
     """
-    if im.mode in ("P", "L") and info and info.get("optimize"):
+    if (
+        im.mode in ("P", "L")
+        and info
+        and info.get("optimize")
+        and im.width != 0
+        and im.height != 0
+    ):
         # Potentially expensive operation.
 
         # The palette saves 3 bytes per color not used, but palette