bug fix, in some case stream reading functions may block indefinitely.

Author: yiqin.li

lib/private/Preview/Movie.php

@@ -144,6 +144,8 @@ private function generateThumbNail(int $maxX, int $maxY, string $absPath, int $s
 		$returnCode = -1;
 		$output = "";
 		if (is_resource($proc)) {
+			stream_set_blocking($pipes[1], 0);
+			stream_set_blocking($pipes[2], 0);
 			$stdout = trim(stream_get_contents($pipes[1]));
 			$stderr = trim(stream_get_contents($pipes[2]));
 			$returnCode = proc_close($proc);