Bug when right-click scrolling past the map edge

[lmoureaux]

On a WRAPX map of size (XSIZE, YSIZE), center the view somewhere near (XSIZE - 5, YSIZE - 10). Then right-click a tile past the map boundary, say (YSIZE - 10, 1). The view gets centered somewhere off-limits, around a position that would be (1, -10).