remote: fix uninitialized variable

Detected by gcc -O2:

remote/remote_driver.c: In function 'doRemoteOpen':
remote/remote_driver.c:2753:26: error: 'sasl' may be used uninitialized in this function [-Werror=uninitialized]

* src/remote/remote_driver.c (remoteAuthSASL): Initialize sasl.

src/remote/remote_driver.c

@@ -2520,7 +2520,7 @@ remoteAuthSASL (virConnectPtr conn, struct private_data *priv,
     int ret = -1;
     const char *mechlist;
     virNetSASLContextPtr saslCtxt;
-    virNetSASLSessionPtr sasl;
+    virNetSASLSessionPtr sasl = NULL;
 
     VIR_DEBUG("Client initialize SASL authentication");