Enable limitation by default as it increases performance

Signed-off-by: Joas Schilling <coding@schilljs.com>

lib/Config.php

@@ -394,8 +394,8 @@ class Config {
 		return hash_equals($hash, substr($ticket, $lastColon + 1));
 	}
 
-	public function getGridVideosLimit(): string {
-		return $this->config->getAppValue('spreed', 'grid_videos_limit', '0');
+	public function getGridVideosLimit(): int {
+		return (int) $this->config->getAppValue('spreed', 'grid_videos_limit', '19'); // 5*4 - self
 	}
 
 	public function getGridVideosLimitEnforced(): bool {