Handle map reset when the game is loaded/unloaded.

https://github.com/dcs-liberation/dcs_liberation/issues/2039

Partial fix for
https://github.com/dcs-liberation/dcs_liberation/issues/2045 (now works
in the new map, old one not fixed yet).

client/src/api/mapSlice.ts

@@ -0,0 +1,30 @@
+import { RootState } from "../app/store";
+import { gameLoaded, gameUnloaded } from "./actions";
+import { createSlice } from "@reduxjs/toolkit";
+import { LatLngLiteral } from "leaflet";
+
+interface MapState {
+  center: LatLngLiteral;
+}
+
+const initialState: MapState = {
+  center: { lat: 0, lng: 0 },
+};
+
+const mapSlice = createSlice({
+  name: "map",
+  initialState: initialState,
+  reducers: {},
+  extraReducers: (builder) => {
+    builder.addCase(gameLoaded, (state, action) => {
+      state.center = action.payload.map_center;
+    });
+    builder.addCase(gameUnloaded, (state) => {
+      state.center = { lat: 0, lng: 0 };
+    });
+  },
+});
+
+export const selectMapCenter = (state: RootState) => state.map.center;
+
+export default mapSlice.reducer;