Avoid file system access on checking if an image exists

Signed-off-by: Julius Härtl <jus@bitgrid.net>

apps/theming/lib/ImageManager.php

@@ -78,10 +78,8 @@ public function __construct(IConfig $config,
 
 	public function getImageUrl(string $key, bool $useSvg = true): string {
 		$cacheBusterCounter = $this->config->getAppValue('theming', 'cachebuster', '0');
-		try {
-			$image = $this->getImage($key, $useSvg);
+		if ($this->hasImage($key)) {
 			return $this->urlGenerator->linkToRoute('theming.Theming.getImage', [ 'key' => $key ]) . '?v=' . $cacheBusterCounter;
-		} catch (NotFoundException $e) {
 		}
 
 		switch ($key) {
@@ -131,6 +129,11 @@ public function getImage(string $key, bool $useSvg = true): ISimpleFile {
 		return $folder->getFile($key);
 	}
 
+	public function hasImage(string $key): bool {
+		$mimeSetting = $this->config->getAppValue('theming', $key . 'Mime', '');
+		return $mimeSetting !== '';
+	}
+
 	public function getCustomImages(): array {
 		$images = [];
 		foreach ($this->supportedImageKeys as $key) {