re-establish null pointer if IMC/IMV manager plugin could not be installed

src/libcharon/plugins/tnc_imc/tnc_imc_plugin.c

@@ -171,6 +171,7 @@ plugin_t *tnc_imc_plugin_create()
 	if (!load_imcs(tnc_config))
 	{
 		charon->imcs->destroy(charon->imcs);
+		charon->imcs = NULL;
 		free(this);
 		return NULL;
 	}

src/libcharon/plugins/tnc_imv/tnc_imv_plugin.c

@@ -172,6 +172,7 @@ plugin_t *tnc_imv_plugin_create()
 	if (!load_imvs(tnc_config))
 	{
 		charon->imvs->destroy(charon->imvs);
+		charon->imvs = NULL;
 		free(this);
 		return NULL;
 	}