[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>
diff --git a/fs/cifs/CHANGES b/fs/cifs/CHANGES
index b486898..3a9b7a5 100644
--- a/fs/cifs/CHANGES
+++ b/fs/cifs/CHANGES
@@ -5,7 +5,7 @@
 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
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