prevent OOB write for BGM fix in grotto mixed pools (#5572)

soh/soh/Enhancements/randomizer/randomizer_entrance.c

@@ -253,10 +253,12 @@ void Entrance_Init(void) {
             for (s16 i = 0; i < 4; i++) {
                 // Zero out the bit in the field which tells the game to keep playing
                 // background music for all four scene setups at each index
+                if (override + i < ENTRANCE_TABLE_SIZE) {
                     gEntranceTable[override + i].field &= ~ENTRANCE_INFO_CONTINUE_BGM_FLAG;
                 }
             }
         }
+    }
 
     hasModifiedEntranceTable = 1;
 }