CLI: add missing file notmuch-client-init

This file should have been created in commit 5a8d174f, but wasn't.

notmuch-client-init.c

@@ -0,0 +1,18 @@
+#include "notmuch-client.h"
+#include "gmime-filter-reply.h"
+
+/* Caller is responsible for only calling this once */
+
+void
+notmuch_client_init (void)
+{
+#if ! GLIB_CHECK_VERSION (2, 35, 1)
+    g_type_init ();
+#endif
+
+    g_mime_init ();
+
+    g_mime_filter_reply_module_init ();
+
+    talloc_enable_null_tracking ();
+}