qemu: Don't access uninitialized memory

In qemuConnectDomainXMLToNative() we set up the monitor, but we never
memset() it to zeros.  Thanks to the introduction of the logfile
parameter of chardevs (and the logfile member of the struct), we started
checking whether that's non-NULL and that exposed this old error.
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

src/qemu/qemu_driver.c

@@ -6950,7 +6950,7 @@ static char *qemuConnectDomainXMLToNative(virConnectPtr conn,
 {
     virQEMUDriverPtr driver = conn->privateData;
     virDomainDefPtr def = NULL;
-    virDomainChrSourceDef monConfig;
+    virDomainChrSourceDef monConfig = {0};
     virQEMUCapsPtr qemuCaps = NULL;
     bool monitor_json = false;
     virCommandPtr cmd = NULL;