Return an empty bytestring from tobytes() for an empty image

Tests/test_image.py

@@ -786,6 +786,11 @@ def test_exif_load_from_fp(self):
                 34665: 196,
             }
 
+    @pytest.mark.parametrize("size", ((1, 0), (0, 1), (0, 0)))
+    def test_zero_tobytes(self, size):
+        im = Image.new("RGB", size)
+        assert im.tobytes() == b""
+
     def test_categories_deprecation(self):
         with pytest.warns(DeprecationWarning):
             assert hopper().category == 0

src/PIL/Image.py

@@ -707,6 +707,9 @@ def tobytes(self, encoder_name="raw", *args):
         :returns: A :py:class:`bytes` object.
         """
 
+        if self.width == 0 or self.height == 0:
+            return b""
+
         # may pass tuple instead of argument list
         if len(args) == 1 and isinstance(args[0], tuple):
             args = args[0]