Change default exclusion list from undefined to empty array

After the recent changes that made the exclusion list global instead of
game specific, and changed it to be loaded on app startup, using
undefined as the default is no longer needed and only makes the typing
awkward.

src/store/modules/TsModsModule.ts

@@ -20,7 +20,7 @@ export interface CachedMod {
 interface State {
     cache: Map<string, CachedMod>;
     deprecated: Map<string, boolean>;
-    exclusions?: string[];
+    exclusions: string[];
     isThunderstoreModListUpdateInProgress: boolean;
     mods: ThunderstoreMod[];
     modsLastUpdated?: Date;
@@ -54,7 +54,7 @@ export const TsModsModule = {
         cache: new Map<string, CachedMod>(),
         deprecated: new Map<string, boolean>(),
         /*** Packages available through API that should be ignored by the manager */
-        exclusions: undefined,
+        exclusions: [],
         /*** Mod list is updated from the API automatically and by user action */
         isThunderstoreModListUpdateInProgress: false,
         /*** All mods available through API for the current active game */
@@ -334,7 +334,7 @@ export const TsModsModule = {
             {chunks, indexHash}: {chunks: PackageListChunks, indexHash: string}
         ) {
             const filtered = chunks.map((chunk) => chunk.filter(
-                (pkg) => !state.exclusions!.includes(pkg.full_name)
+                (pkg) => !state.exclusions.includes(pkg.full_name)
             ));
             const community = rootState.activeGame.internalFolderName;
             await PackageDb.updateFromApiResponse(community, filtered);