minor-bug: LOAD_STR() should end if null
minor-bug: LOAD_STR() should end if null

There was a small bug in the LOAD_STR() macro which would cause it to
read beyond the limit of the string because it wasn't testing for
p = '\0'.

The reason it didn't crash anything was because the buffer was already
continious space, so  other than the very last call, there was no chance
of a segfault

chloridite/OpenBoardView,MattSturgeon/OpenBoardView,chloridite/OpenBoardView,MattSturgeon/OpenBoardView