util: fix leaks in wmsetbg's changeTextureForWorkspace (Coverity #50169)
As pointed by Coverity, some locally created PropList objects are not freed
when the function returns. The truth is their refCount is 1 more than what
they should be, but that's more than what Coverity can detect today.
This patch adds the appropriate release calls when they are not needed
anymore, which will actually not free them but get their refCount right so
they will be freed as soon as the PropList in which they are used are
released.
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>