SwitchPanel: make sure WMRetainColor and WMReleaseColor calls are even
The number of calls to WMRetainColor for a color in use should the same as the number of calls to WMReleaseColor
to free that color. In case of discrepancy, random crashes can happen and memory is not freed properly.
To debug that issue I checked the retained colors when the switchpanel is opened and then checked if those colors are properly released once the panel is closed.
This patch fixes the issue mentioned at https://github.com/window-maker/wmaker/issues/22