make sure that the urls for theming images are valid

In some circumstances the url generation seems to fail,
resulting in an empty image url which causes the browser to load the main
page multiple times, leading to issues with state tokens

Signed-off-by: Robin Appelman <robin@icewind.nl>

apps/theming/lib/ThemingDefaults.php

@@ -334,11 +334,12 @@ class ThemingDefaults extends \OC_Defaults {
 			$customFavicon = null;
 		}
 
+		$route = false;
 		if ($image === 'favicon.ico' && ($customFavicon !== null || $this->imageManager->shouldReplaceIcons())) {
-			return $this->urlGenerator->linkToRoute('theming.Icon.getFavicon', ['app' => $app]) . '?v=' . $cacheBusterValue;
+			$route = $this->urlGenerator->linkToRoute('theming.Icon.getFavicon', ['app' => $app]);
 		}
 		if ($image === 'favicon-touch.png' && ($customFavicon !== null || $this->imageManager->shouldReplaceIcons())) {
-			return $this->urlGenerator->linkToRoute('theming.Icon.getTouchIcon', ['app' => $app]) . '?v=' . $cacheBusterValue;
+			$route = $this->urlGenerator->linkToRoute('theming.Icon.getTouchIcon', ['app' => $app]);
 		}
 		if ($image === 'manifest.json') {
 			try {
@@ -347,11 +348,16 @@ class ThemingDefaults extends \OC_Defaults {
 					return false;
 				}
 			} catch (AppPathNotFoundException $e) {}
-			return $this->urlGenerator->linkToRoute('theming.Theming.getManifest') . '?v=' . $cacheBusterValue;
+			$route = $this->urlGenerator->linkToRoute('theming.Theming.getManifest');
 		}
 		if (strpos($image, 'filetypes/') === 0 && file_exists(\OC::$SERVERROOT . '/core/img/' . $image )) {
-			return $this->urlGenerator->linkToRoute('theming.Icon.getThemedIcon', ['app' => $app, 'image' => $image]);
+			$route = $this->urlGenerator->linkToRoute('theming.Icon.getThemedIcon', ['app' => $app, 'image' => $image]);
 		}
+
+		if ($route) {
+			return $route . '?v=' . $cacheBusterValue;
+		}
+
 		return false;
 	}