Fixed issue #6649 by checking for internet connection before starting the game if "online multiplayer" is selected

Many thanks to @SomeTroglodyte for most of the code and for explanations

desktop/src/com/unciv/app/desktop/PlatformSpecificHelpersDesktop.kt

@@ -11,7 +11,7 @@ class PlatformSpecificHelpersDesktop : GeneralPlatformSpecificHelpers {
     override fun isInternetConnected(): Boolean {
         return try {
             InetAddress.getByName("8.8.8.8").isReachable(500)  // Parameter timeout in milliseconds
-        }catch (ex: Exception){
+        } catch (ex: Throwable) {
             false
         }
     }