Merge pull request #18475 from nextcloud/backport/18456/stable17

[stable17] Fix Office preview generation

Author: rullzer

lib/private/Preview/Office.php

@@ -56,7 +56,7 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 		$pngPreview = null;
 		try {
 			list($dirname, , , $filename) = array_values(pathinfo($absPath));
-			$pngPreview = $dirname . '/' . $filename . '.png';
+			$pngPreview = $tmpDir . '/' . $filename . '.png';
 
 			$png = new \imagick($pngPreview . '[0]');
 			$png->setImageFormat('jpg');