Fix checkpointer PANIC due to missing fsync cancel in mdunlinkfork()

Add missing register_forget_request() in the 'else' branch of
mdunlinkfork(), before register_unlink_segment(), matching what the
'if' branch already does.

Author: Satyanarayana Narlapuram

src/backend/storage/smgr/md.c

@@ -418,6 +418,11 @@ mdunlinkfork(RelFileLocatorBackend rlocator, ForkNumber forknum, bool isRedo)
 		/* Prevent other backends' fds from holding on to the disk space */
 		ret = do_truncate(path.str);
 
+		/* Forget any pending sync requests for the first segment */
+		save_errno = errno;
+		register_forget_request(rlocator, forknum, 0 /* first seg */ );
+		errno = save_errno;
+
 		/* Register request to unlink first segment later */
 		save_errno = errno;
 		register_unlink_tombstone(rlocator);