[CIFS] Do not send tree disconnect if session is already disconnected

Noticed this when tree connect timed out (due to Samba server crash) -
we try to send a tree disconnect for a tid that does not exist
since we don't have a valid tree id yet. This checks that the
session is valid before sending the tree disconnect to handle
this case.
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/CHANGES

@@ -5,7 +5,7 @@ client generated ones by default (mount option "serverino" turned
 on by default if server supports it).  Add forceuid and forcegid
 mount options (so that when negotiating unix extensions specifying
 which uid mounted does not immediately force the server's reported
-uids to be overridden).
+uids to be overridden).  Add support for scope moutn parm.
 
 Version 1.58
 ------------

fs/cifs/cifssmb.c

@@ -729,7 +729,7 @@ CIFSSMBTDis(const int xid, struct cifsTconInfo *tcon)
 	 * the tcon is no longer on the list, so no need to take lock before
 	 * checking this.
 	 */
-	if (tcon->need_reconnect)
+	if ((tcon->need_reconnect) || (tcon->ses->need_reconnect))
 		return 0;
 
 	rc = small_smb_init(SMB_COM_TREE_DISCONNECT, 0, tcon,