fix(ViewController): Regression lead to 500 on non-existent fileIds

Fixes #42418 

Signed-off-by: Josh Richards <josh.t.richards@gmail.com>

apps/files/lib/Controller/ViewController.php

@@ -237,12 +237,16 @@ class ViewController extends Controller {
 		if ($fileid && $dir !== '') {
 			$baseFolder = $this->rootFolder->getUserFolder($userId);
 			$nodes = $baseFolder->getById((int) $fileid);
-			$nodePath = $baseFolder->getRelativePath($nodes[0]->getPath());
-			$relativePath = $nodePath ? dirname($nodePath) : '';
-			// If the requested path does not contain the file id
-			// or if the requested path is not the file id itself
-			if (count($nodes) === 1 && $relativePath !== $dir && $nodePath !== $dir) {
-				return $this->redirectToFile((int) $fileid);
+			if (!empty($nodes)) {
+				$nodePath = $baseFolder->getRelativePath($nodes[0]->getPath());
+				$relativePath = $nodePath ? dirname($nodePath) : '';
+				// If the requested path does not contain the file id
+				// or if the requested path is not the file id itself
+				if (count($nodes) === 1 && $relativePath !== $dir && $nodePath !== $dir) {
+					return $this->redirectToFile((int) $fileid);
+				}
+			} else { // fileid does not exist anywhere
+				$fileNotFound = true;
 			}
 		}