Fix dereference before null check warning

null tcon is not likely in these paths in current
code, but obviously it does clarify the code to
check for null (if at all) before derefrencing
rather than after.

Reported by Coverity (CID 1042666)
Signed-off-by: Steve French <smfrench@gmail.com>
Acked-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Acked-by: Sachin Prabhu <sprabhu@redhat.com>

fs/cifs/smb2pdu.c

@@ -1218,7 +1218,7 @@ SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	struct smb2_ioctl_req *req;
 	struct smb2_ioctl_rsp *rsp;
 	struct TCP_Server_Info *server;
-	struct cifs_ses *ses = tcon->ses;
+	struct cifs_ses *ses;
 	struct kvec iov[2];
 	int resp_buftype;
 	int num_iovecs;
@@ -1233,6 +1233,11 @@ SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	if (plen)
 		*plen = 0;
 
+	if (tcon)
+		ses = tcon->ses;
+	else
+		return -EIO;
+
 	if (ses && (ses->server))
 		server = ses->server;
 	else
@@ -1296,14 +1301,12 @@ SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	rsp = (struct smb2_ioctl_rsp *)iov[0].iov_base;
 
 	if ((rc != 0) && (rc != -EINVAL)) {
-		if (tcon)
-			cifs_stats_fail_inc(tcon, SMB2_IOCTL_HE);
+		cifs_stats_fail_inc(tcon, SMB2_IOCTL_HE);
 		goto ioctl_exit;
 	} else if (rc == -EINVAL) {
 		if ((opcode != FSCTL_SRV_COPYCHUNK_WRITE) &&
 		    (opcode != FSCTL_SRV_COPYCHUNK)) {
-			if (tcon)
-				cifs_stats_fail_inc(tcon, SMB2_IOCTL_HE);
+			cifs_stats_fail_inc(tcon, SMB2_IOCTL_HE);
 			goto ioctl_exit;
 		}
 	}