Don't clobber CHR RAM limit estimation on MMC3 restore

src/map/mmc3.c

@@ -376,7 +376,9 @@ static int mmc3_state_read(void* _map, const void* data,
     int base_size = mmc3_state_size(map) - map->chr_ram_lim;
     int size = base_size + mmc3_chr_ram_size(map);
     if (size > data_len) size = data_len;
-    map->chr_ram_lim = data_len - base_size;
+    if (data_len - base_size > map->chr_ram_lim) {
+        map->chr_ram_lim = data_len - base_size;
+    }
     memcpy(map->r, data, size);
 
     uint8_t new_bank_select = map->bank_select;