[CIFS] Fix oops in reset_cifs_unix_caps on reconnect

Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/connect.c

@@ -1670,7 +1670,7 @@ void reset_cifs_unix_caps(int xid, struct cifsTconInfo * tcon,
 		/* We might be setting the path sep back to a different
 		form if we are reconnecting and the server switched its
 		posix path capability for this share */	
-		if(CIFS_SB(sb)->prepathlen > 0)
+		if(sb && (CIFS_SB(sb)->prepathlen > 0))
 			CIFS_SB(sb)->prepath[0] = CIFS_DIR_SEP(CIFS_SB(sb));
 	
 		cFYI(1,("Negotiate caps 0x%x",(int)cap));