libvirt: Increase connection reference count for callbacks

By adjusting the reference count of the connection object we
prevent races between callback function and virConnectClose.
Signed-off-by: NViktor Mihajlovski <mihajlov@linux.vnet.ibm.com>

src/libvirt.c

@@ -20186,6 +20186,8 @@ int virConnectRegisterCloseCallback(virConnectPtr conn,
         return -1;
     }
 
+    virObjectRef(conn);
+
     virMutexLock(&conn->lock);
 
     virCheckNonNullArgGoto(cb, error);
@@ -20206,6 +20208,7 @@ int virConnectRegisterCloseCallback(virConnectPtr conn,
 
 error:
     virMutexUnlock(&conn->lock);
+    virObjectUnref(conn);
     virDispatchError(NULL);
     return -1;
 }
@@ -20255,6 +20258,8 @@ int virConnectUnregisterCloseCallback(virConnectPtr conn,
 
     virMutexUnlock(&conn->lock);
 
+    virObjectUnref(conn);
+
     return 0;
 
 error: