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)

src/r_segs.c

@@ -706,10 +706,10 @@ void R_RenderMaskedSegRange(drawseg_t *ds, INT32 x1, INT32 x2)
 // Loop through R_DrawMaskedColumn calls
 static void R_DrawRepeatMaskedColumn(column_t *col)
 {
-	do {
+	while (sprtopscreen < sprbotscreen) {
 		R_DrawMaskedColumn(col);
 		sprtopscreen += dc_texheight*spryscale;
-	} while (sprtopscreen < sprbotscreen);
+	}
 }
 
 //