MDDialog hover state change disregards custom md_bg_color

[ddauer]

When opening a simple dialog with a custom md_bg_color, a mouse exit will kill the md_bg_color (by setting it to transparent or something).

MDDialog(            
	MDDialogContentContainer(
		MDIcon(icon="weight")
	),
   	theme_bg_color = "Custom",
	md_bg_color = "red",
).open()

This is due to https://github.com/kivymd/KivyMD/blob/cfe5aac30f50708c6208c8b33b0ef1aa390721e8/kivymd/uix/card/card.py#L682

Disable this line, and the md_bg_color will stay red onMouseOut (as expected)