migration: Free the error earlier in the resume case

Freeing the error at migration_connect() is redundant in the normal
migration case. The freeing already happened at migrate_init():

qmp_migrate()
-> migrate_prepare()
   -> migrate_init()
-> qmp_migrate_finish()
   -> *_start_outgoing_migration()
   -> migration_channel_connect()
      -> migration_connect()

For the resume case, migrate_prepare() returns early and doesn't reach
migrate_init(). Move the extra migrate_error_free() call to
migrate_prepare() along with the resume check.

Also change migrate_init() to use migrate_error_free(), so it's easier
to see where are the places the error gets freed.

Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Prasad Pandit <pjp@fedoraproject.org>
Link: https://lore.kernel.org/qemu-devel/20260123141656.6765-8-farosas@suse.de
Signed-off-by: Fabiano Rosas <farosas@suse.de>

migration/migration.c

@@ -1808,8 +1808,8 @@ int migrate_init(MigrationState *s, Error **errp)
     s->setup_time = 0;
     s->start_postcopy = false;
     s->migration_thread_running = false;
-    error_free(s->error);
-    s->error = NULL;
+
+    migrate_error_free(s);
 
     if (should_send_vmdesc()) {
         s->vmdesc = json_writer_new(false);
@@ -2084,6 +2084,13 @@ static bool migrate_prepare(MigrationState *s, bool resume, Error **errp)
         migrate_set_state(&s->state, MIGRATION_STATUS_POSTCOPY_PAUSED,
                           MIGRATION_STATUS_POSTCOPY_RECOVER_SETUP);
 
+        /*
+         * If there's a previous error, free it and prepare for
+         * another one. For the non-resume case, this happens at
+         * migrate_init() below.
+         */
+        migrate_error_free(s);
+
         /* This is a resume, skip init status */
         return true;
     }
@@ -4007,13 +4014,6 @@ void migration_connect(MigrationState *s, Error *error_in)
     bool resume = (s->state == MIGRATION_STATUS_POSTCOPY_RECOVER_SETUP);
     int ret;
 
-    /*
-     * If there's a previous error, free it and prepare for another one.
-     * Meanwhile if migration completes successfully, there won't have an error
-     * dumped when calling migration_cleanup().
-     */
-    migrate_error_free(s);
-
     s->expected_downtime = migrate_downtime_limit();
     if (error_in) {
         migration_connect_error_propagate(s, error_in);