Read theme only if required

lib/private/urlgenerator.php

@@ -117,15 +117,15 @@ class URLGenerator implements IURLGenerator {
 	 * Returns the path to the image.
 	 */
 	public function imagePath($app, $image) {
-		// Read the selected theme from the config file
-		$theme = \OC_Util::getTheme();
-
 		$cache = $this->cacheFactory->create('imagePath');
 		$cacheKey = $app.'-'.$image;
 		if($cache->hasKey($cacheKey)) {
 			return $cache->get($cacheKey);
 		}
 
+		// Read the selected theme from the config file
+		$theme = \OC_Util::getTheme();
+
 		//if a theme has a png but not an svg always use the png
 		$basename = substr(basename($image),0,-4);