parallels: fix libvirt crash if parallelsNetworkOpen fails

If, by any reason, parallelsNetworkOpen fails it dereferences
newly allocated privconn->networks via virObjectUnref, which in
turn deallocates its memory.
Subsequent call of parallelsNetworkClose calls virObjectUnref
that leads to double memory free. To prevent this we should zero
privconn->networks to make all subsequent virObjectUnref be safe.

Signed-off-by: Maxim Nestratov <mnestratov@parallels.com>

src/parallels/parallels_network.c

@@ -348,6 +348,7 @@ parallelsNetworkOpen(virConnectPtr conn,
     return VIR_DRV_OPEN_SUCCESS;
  error:
     virObjectUnref(privconn->networks);
+    privconn->networks = NULL;
     return VIR_DRV_OPEN_DECLINED;
 }