Fix, prevent NPE in FileSystems#getFileSystem when default game URI i…

…s missing a scheme (#8058)

Bug report #8015 has a NPE in getFileSystem, this looks to happen if the default
game URI is missing a scheme. That can be something trivial like an empty
value for the default game URI (empty but not null), or could be caused by
other reasons.

Regardless, instead of throwing an exception in such cases, we can fall back to resetting
the default game to a default value.

game-core/src/main/java/games/strategy/engine/framework/startup/ui/panels/main/game/selector/GameSelectorModel.java

@@ -23,6 +23,7 @@
 import java.util.Observable;
 import java.util.Optional;
 import java.util.function.Function;
+import java.util.function.Predicate;
 import javax.annotation.Nullable;
 import lombok.Getter;
 import lombok.Setter;
@@ -204,19 +205,31 @@ public void onGameEnded() {
   public void loadDefaultGameSameThread() {
     ClientSetting.defaultGameUri
         .getValue()
+        .filter(Predicate.not(String::isBlank))
+        .filter(GameSelectorModel::gameUriExistsOnFileSystem)
         .map(URI::create)
-        // we don't want to load a game file by default that is not within the map folders we
-        // can load. (ie: if a previous version of triplea was using running a game within its
-        // root folder, we shouldn't open it)
-        .filter(
-            defaultGame ->
-                getDefaultGameRealPath(defaultGame)
-                    .startsWith(ClientFileSystemHelper.getUserRootFolder().toPath()))
-        // ensure the default game hasn't been deleted since it was last loaded
-        .filter(defaultGame -> getDefaultGameRealPath(defaultGame).toFile().exists())
         .ifPresentOrElse(this::load, this::resetDefaultGame);
   }
 
+  @SuppressWarnings("ReturnValueIgnored")
+  private static boolean gameUriExistsOnFileSystem(final String gameUri) {
+    try {
+      Path.of(URI.create(gameUri));
+    } catch (final IllegalArgumentException ignored) {
+      // thrown if the URI is invalid (EG: missing URI scheme)
+      return false;
+    }
+
+    final Path realPath = getDefaultGameRealPath(URI.create(gameUri));
+
+    // starts with check is because we don't want to load a game file by default that is not within
+    // the map folders. (ie: if a previous version of triplea was using running a game within its
+    // root folder, we shouldn't open it)
+
+    return realPath.startsWith(ClientFileSystemHelper.getUserRootFolder().toPath())
+        && realPath.toFile().exists();
+  }
+
   /**
    * Determine the real path of the default game.
    *