Unlock when promoting to exclusive lock fails

In certain cases changeLock to EXCLUSIVE fails
and throws LockedException. This leaves the
file locked as SHARED in file_put_contents,
which prevents retrying (because on second
call file_put_contents takes another SHARED
lock on the same file, and changeLock doesn't
allow more than a single SHARED lock to promote
to EXCLUSIVE).

To avoid this case, we catch the LockedException
and unlock before re-throwing.

Signed-off-by: Ashod Nakashian <ashod.nakashian@collabora.co.uk>

lib/private/Files/View.php

@@ -665,7 +665,13 @@ class View {
 					return false;
 				}
 
+				try {
 					$this->changeLock($path, ILockingProvider::LOCK_EXCLUSIVE);
+				} catch (\Exception $e) {
+					// Release the shared lock before throwing.
+					$this->unlockFile($path, ILockingProvider::LOCK_SHARED);
+					throw $e;
+				}
 
 				/** @var \OC\Files\Storage\Storage $storage */
 				list($storage, $internalPath) = $this->resolvePath($path);