Explicitly zero declared struct ScreenSettingss

Performance cost is negligible and well worth being safe in case there
are more members added in the future but we forget to initialize them.

desktop_version/src/Game.cpp

@@ -4328,6 +4328,7 @@ void Game::deserializesettings(tinyxml2::XMLElement* dataNode, struct ScreenSett
 bool Game::savestats(bool sync /*= true*/)
 {
     struct ScreenSettings screen_settings;
+    SDL_zero(screen_settings);
     gameScreen.GetSettings(&screen_settings);
 
     return savestats(&screen_settings, sync);
@@ -4593,6 +4594,7 @@ void Game::loadsettings(struct ScreenSettings* screen_settings)
 bool Game::savesettings(void)
 {
     struct ScreenSettings screen_settings;
+    SDL_zero(screen_settings);
     gameScreen.GetSettings(&screen_settings);
 
     return savesettings(&screen_settings);

desktop_version/src/main.cpp

@@ -572,6 +572,7 @@ int main(int argc, char *argv[])
         // Prioritize unlock.vvv first (2.2 and below),
         // but settings have been migrated to settings.vvv (2.3 and up)
         struct ScreenSettings screen_settings;
+        SDL_zero(screen_settings);
         ScreenSettings_default(&screen_settings);
         game.loadstats(&screen_settings);
         game.loadsettings(&screen_settings);