port: another UB fix in bg.c

src/game/bg.c

@@ -4378,7 +4378,11 @@ bool bgTestHitInVtxBatch(struct coord *arg0, struct coord *arg1, struct coord *a
 												texturenum = *(s16 *) PHYS_TO_K0(tmp);
 											}
 
+#ifdef AVOID_UB
+											if (batch->type == VTXBATCHTYPE_XLU && texturenum >= 0 && g_Textures[texturenum].surfacetype == SURFACETYPE_DEFAULT) {
+#else
 											if (batch->type == VTXBATCHTYPE_XLU && g_Textures[texturenum].surfacetype == SURFACETYPE_DEFAULT) {
+#endif
 												hit = false;
 											}