Cygwin: lockf: Fix adding a new lock over multiple locks

Previously, adding a new lock by lockf() over multiple existing locks
failed. This is due to a bug that lf_setlock() tries to create a lock
that has already been created. This patch fixes the issue.

Addresses: https://cygwin.com/pipermail/cygwin/2024-October/256528.html
Fixes: a998dd7055 ("* flock.cc: Implement all advisory file locking here.")
Reported-by: Christian Franke <Christian.Franke@t-online.de>
Reviewed-by: Corinna Vinschen <corinna@vinschen.de>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

winsup/cygwin/flock.cc

@@ -1454,13 +1454,14 @@ lf_setlock (lockf_t *lock, inode_t *node, lockf_t **clean, HANDLE fhdl)
 	  /*
 	   * Add the new lock before overlap.
 	   */
-	  if (needtolink) {
+	  if (needtolink)
+	    {
 	      *prev = lock;
 	      lock->lf_next = overlap;
-	  }
+	      lock->create_lock_obj ();
+	    }
 	  overlap->lf_start = lock->lf_end + 1;
 	  lf_wakelock (overlap, fhdl);
-	  lock->create_lock_obj ();
 	  overlap->create_lock_obj ();
 	  break;
 	}

winsup/cygwin/release/3.5.5

@@ -12,3 +12,7 @@ Fixes:
   Addresses: https://sourceware.org/pipermail/cygwin/2024-September/256468.html
 
 - Fix timer_delete() return value which always indicated failure.
+
+- Fix lockf() error which occurs when adding a new lock over multiple
+  locks.
+  Addresses: https://cygwin.com/pipermail/cygwin/2024-October/256528.html