fix(theming): display error messages on image upload and delete previous image only after validation

Signed-off-by: Cristian Scheid <cristianscheid@gmail.com>

Author: cristianscheid

apps/theming/lib/ImageManager.php

@@ -202,8 +202,6 @@ public function delete(string $key): void {
 	}
 
 	public function updateImage(string $key, string $tmpFile): string {
-		$this->delete($key);
-
 		try {
 			$folder = $this->getRootFolder()->getFolder('images');
 		} catch (NotFoundException $e) {
@@ -217,6 +215,8 @@ public function updateImage(string $key, string $tmpFile): string {
 			throw new \Exception('Unsupported image type: ' . $detectedMimeType);
 		}
 
+		$this->delete($key);
+
 		if ($key === 'background') {
 			if ($this->shouldOptimizeBackgroundImage($detectedMimeType, filesize($tmpFile))) {
 				try {