Check whether output buffering is active before turning it off

Before we just turned it off and @Suppressed the error if ob was not active.
In PHP 8 this error is no longer suppressed, so try to not cause it at all.

Signed-off-by: Richard de Boer <git@tubul.net>

lib/private/Files/View.php

@@ -422,7 +422,9 @@ public function filesize($path) {
 	 */
 	public function readfile($path) {
 		$this->assertPathLength($path);
-		@ob_end_clean();
+		if (ob_get_level()) {
+			ob_end_clean();
+		}
 		$handle = $this->fopen($path, 'rb');
 		if ($handle) {
 			$chunkSize = 524288; // 512 kB chunks
@@ -446,7 +448,9 @@ public function readfile($path) {
 	 */
 	public function readfilePart($path, $from, $to) {
 		$this->assertPathLength($path);
-		@ob_end_clean();
+		if (ob_get_level()) {
+			ob_end_clean();
+		}
 		$handle = $this->fopen($path, 'rb');
 		if ($handle) {
 			$chunkSize = 524288; // 512 kB chunks