qemuDomainGetGuestInfo: don't assign NULL hostname

Don't rely on error check and assign hostname only when non-NULL.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_driver.c

@@ -22967,14 +22967,14 @@ qemuDomainGetGuestInfo(virDomainPtr dom,
     }
     if (supportedTypes & VIR_DOMAIN_GUEST_INFO_HOSTNAME) {
         rc = qemuAgentGetHostname(agent, &hostname);
-        if (rc < 0 && !(rc == -2 && types == 0)) {
-            goto exitagent;
-        } else {
-            if (virTypedParamsAddString(params, nparams, &maxparams, "hostname",
-                                        hostname) < 0)
+        if (rc < 0 && !(rc == -2 && types == 0))
             goto exitagent;
     }
-    }
+
+    if (hostname &&
+        virTypedParamsAddString(params, nparams, &maxparams, "hostname", hostname) < 0)
+        goto exitagent;
+
     if (supportedTypes & VIR_DOMAIN_GUEST_INFO_FILESYSTEM) {
         rc = qemuAgentGetFSInfo(agent, &agentfsinfo);
         if (rc < 0) {