Properly use user background cachebuster

Signed-off-by: John Molakvoæ <skjnldsv@protonmail.com>

apps/theming/lib/ImageManager.php

@@ -106,9 +106,11 @@ class ImageManager {
 	public function getImage(string $key, bool $useSvg = true): ISimpleFile {
 		$logo = $this->config->getAppValue('theming', $key . 'Mime', '');
 		$folder = $this->getRootFolder()->getFolder('images');
+
 		if ($logo === '' || !$folder->fileExists($key)) {
 			throw new NotFoundException();
 		}
+
 		if (!$useSvg && $this->shouldReplaceIcons()) {
 			if (!$folder->fileExists($key . '.png')) {
 				try {
@@ -126,6 +128,7 @@ class ImageManager {
 				return $folder->getFile($key . '.png');
 			}
 		}
+
 		return $folder->getFile($key);
 	}
 

apps/theming/lib/Themes/DefaultTheme.php

@@ -239,9 +239,10 @@ class DefaultTheme implements ITheme {
 		$user = $this->userSession->getUser();
 		if ($appManager->isEnabledForUser(Application::APP_ID) && $user !== null) {
 			$themingBackground = $this->config->getUserValue($user->getUID(), Application::APP_ID, 'background', 'default');
+			$currentVersion = (int)$this->config->getUserValue($user->getUID(), Application::APP_ID, 'backgroundVersion', '0');
 
 			if ($themingBackground === 'custom') {
-				$variables['--image-main-background'] = "url('" . $this->urlGenerator->linkToRouteAbsolute('theming.userTheme.getBackground') . "')";
+				$variables['--image-main-background'] = "url('" . $this->urlGenerator->linkToRouteAbsolute('theming.userTheme.getBackground') . "?v=$currentVersion')";
 			} elseif (isset(BackgroundService::SHIPPED_BACKGROUNDS[$themingBackground])) {
 				$variables['--image-main-background'] = "url('" . $this->urlGenerator->linkTo(Application::APP_ID, "/img/background/$themingBackground") . "')";
 			} elseif (substr($themingBackground, 0, 1) === '#') {