Fix endless loop of R_DrawRepeatMaskedColumn if both sprtopscreen and...

Fix endless loop of R_DrawRepeatMaskedColumn if both sprtopscreen and sprbotscreen are CLAMPMAX (INT32_MAX)

This fixes the grid floors in TD's Lava Mountain freezing the game if they go off the bottom of the screen far enough (they have ACWRFL1A as the wall texture, which is a single patch texture with holes)