Prevent error in files_trashbin

`glob` can return FALSE when the directory is empty, instead of an empty array,
causing an error at `foreach`.

"Note: On some systems it is impossible to distinguish between empty match and
an error."

See http://www.php.net/manual/en/function.glob.php -> Return Values

apps/files_trashbin/lib/trashbin.php

@@ -824,6 +824,7 @@ class Trashbin {
 			$matches = glob($escapedVersionsName . '*');
 		}
 
+		if (is_array($matches)) {
 			foreach ($matches as $ma) {
 				if ($timestamp) {
 					$parts = explode('.v', substr($ma, 0, $offset));
@@ -833,6 +834,7 @@ class Trashbin {
 					$versions[] = (end($parts));
 				}
 			}
+		}
 		return $versions;
 	}