initrd: fix use-after-free when multiple iBFT entries fail

The error variable is declared outside the loop but freed with
g_error_free() which does not reset the pointer to NULL. On the
next iteration, g_set_error() sees a non-NULL *err (dangling pointer)
and error->message dereferences freed memory.

Use g_clear_error() instead which also resets the pointer.

Found by Coverity (CID: USE_AFTER_FREE).

Fixes: ecc074b2f8 ('initrd: add command line parser')

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
(cherry picked from commit 33871478b7)

src/nm-initrd-generator/nmi-cmdline-reader.c

@@ -409,7 +409,7 @@ reader_read_all_connections_from_fw(Reader *reader, const char *sysfs_dir)
 
         if (!nmi_ibft_update_connection_from_nic(connection, nic, &error)) {
             _LOGW(LOGD_CORE, "Unable to merge iBFT configuration: %s", error->message);
-            g_error_free(error);
+            g_clear_error(&error);
             continue;
         }