libnm: fix crash during the restart after killed

When cloud-init job (metadata service crawler) starts, it sends the
SIGTERM signal to nm-cloud-setup and force the nm-cloud-setup to
restart, however, because the error is not initialized as NULL in
`_init_start_cancelled_cb()` before it is set, nm-cloud-setup will hit
a dumped core.

TO fix it, initialize the error as NULL in `_init_start_cancelled_cb()`.

https://bugzilla.redhat.com/show_bug.cgi?id=2027674

Fixes: ce0e898fb476 ('libnm: refactor caching of D-Bus objects in NMClient')

Backtrace:

 #0  g_logv (log_domain=0x7f833a872071 "GLib", log_level=G_LOG_LEVEL_WARNING, format=<optimized out>, args=<optimized out>) at ../glib/gmessages.c:1413
 #1  0x00007f833a81f043 in g_log (log_domain=<optimized out>, log_level=<optimized out>, format=<optimized out>) at ../glib/gmessages.c:1451
 #2  0x00007f833ab97230 in nm_utils_error_set_cancelled (is_disposing=<optimized out>, instance_name=<optimized out>, error=0x7ffff79cb980) at src/libnm-glib-aux/nm-shared-utils.c:2599
 #3  nm_utils_error_set_cancelled (is_disposing=0, instance_name=0x0, error=0x7ffff79cb980) at src/libnm-glib-aux/nm-shared-utils.c:2590
 #4  _init_start_cancelled_cb (cancellable=<optimized out>, user_data=0x5640ca292150) at src/libnm-client-impl/nm-client.c:7324
 #5  _init_start_cancelled_cb (cancellable=<optimized out>, user_data=0x5640ca292150) at src/libnm-client-impl/nm-client.c:7307
 #6  0x00007f833a93094a in _g_closure_invoke_va (param_types=0x0, n_params=<optimized out>, args=0x7ffff79cbb40, instance=0x5640ca267020, return_value=0x0, closure=0x5640ca29d430)
     at ../gobject/gclosure.c:873
 #7  g_signal_emit_valist (instance=0x5640ca267020, signal_id=<optimized out>, detail=0, var_args=var_args@entry=0x7ffff79cbb40) at ../gobject/gsignal.c:3406
 #8  0x00007f833a930a93 in g_signal_emit (instance=instance@entry=0x5640ca267020, signal_id=<optimized out>, detail=detail@entry=0) at ../gobject/gsignal.c:3553
 #9  0x00007f833a9a6475 in g_cancellable_cancel (cancellable=0x5640ca267020) at ../gio/gcancellable.c:513
 #10 g_cancellable_cancel (cancellable=0x5640ca267020) at ../gio/gcancellable.c:487
 #11 0x00005640ca1a8bd4 in sigterm_handler (user_data=0x5640ca267020) at src/nm-cloud-setup/main.c:599
 #12 0x00007f833a819d4f in g_main_dispatch (context=0x5640ca268ef0) at ../glib/gmain.c:3337
 #13 g_main_context_dispatch (context=0x5640ca268ef0) at ../glib/gmain.c:4055
 #14 0x00007f833a86e608 in g_main_context_iterate.constprop.0 (context=0x5640ca268ef0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib/gmain.c:4131
 #15 0x00007f833a819463 in g_main_loop_run (loop=0x5640ca24fdb0) at ../glib/gmain.c:4329
 #16 0x00005640ca1a6d04 in nmc_client_new_waitsync (cancellable=0x5640ca267020, out_nmc=0x7ffff79cbfa0, error=0x7ffff79cbf98, first_property_name=0x5640ca1b11db "instance-flags",
     first_property_name=0x5640ca1b11db "instance-flags") at src/libnm-client-aux-extern/nm-libnm-aux.c:129
 #17 0x00005640ca1a3863 in main (argc=1, argv=<optimized out>) at src/nm-cloud-setup/main.c:639

1 files changed, 3 insertions, 3 deletions

diff --git a/src/libnm-client-impl/nm-client.c b/src/libnm-client-impl/nm-client.c
index 123c44c500..f2081aaa25 100644
--- a/src/libnm-client-impl/nm-client.c
+++ b/src/libnm-client-impl/nm-client.c
@@ -7305,9 +7305,9 @@ _init_start_check_complete(NMClient *self)
 static void
 _init_start_cancelled_cb(GCancellable *cancellable, gpointer user_data)
 {
-    NMClient        *self = user_data;
-    NMClientPrivate *priv = NM_CLIENT_GET_PRIVATE(self);
-    GError          *error;
+    NMClient        *self  = user_data;
+    NMClientPrivate *priv  = NM_CLIENT_GET_PRIVATE(self);
+    GError          *error = NULL;
 
     nm_assert(NM_IS_CLIENT(self));
     nm_assert(priv->init_data);