test given coordinates in smart window placement algorithm
test given coordinates in smart window placement algorithm

the coordinates passed to this function were never used or tested for
being a valid placement location, resulting in any clients which started
with a given position being moved to a pre-existing smart placement test
case, usually the upper-left or lower-right corners of the screen

fix T1106

rvandegrift/e,rvandegrift/e,rvandegrift/e