conf: Fix libvirtd free() segfault if virDomainChrSourceDefNew(...) fails

If virDomainChrSourceDefNew(xmlopt) fails, it will lead to free()ing
the uninitialized pointer bus. The fix for this is to initialize bus
with NULL.
Signed-off-by: NMarc Hartmayer <mhartmay@linux.vnet.ibm.com>
Reviewed-by: NBoris Fiuczynski <fiuczy@linux.vnet.ibm.com>
Reviewed-by: NBjoern Walk <bwalk@linux.vnet.ibm.com>

src/conf/domain_conf.c

@@ -13317,7 +13317,7 @@ virDomainRedirdevDefParseXML(virDomainXMLOptionPtr xmlopt,
 {
     xmlNodePtr cur;
     virDomainRedirdevDefPtr def;
-    char *bus, *type = NULL;
+    char *bus = NULL, *type = NULL;
     int remaining;
 
     if (VIR_ALLOC(def) < 0)