domain_nwfilter: Return early if net has no name in virDomainConfNWFilterTeardownImpl

This function is called from various clean up paths (e.g.
from qemuBuildInterfaceCommandLine). However, depending on the
stage the interface creation process failed at, net->ifname might
still be not filled in when control jumps to cleanup label. If
that is the case return early (avoiding useless error message
produced in virNWFilterBindingLookupByPortDev) as there is no
NWFilter to tear down anyway.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

src/conf/domain_nwfilter.c

@@ -133,6 +133,9 @@ virDomainConfNWFilterTeardownImpl(virConnectPtr conn,
 {
     virNWFilterBindingPtr binding;
 
+    if (!net->ifname)
+        return;
+
     binding = virNWFilterBindingLookupByPortDev(conn, net->ifname);
     if (!binding)
         return;