CHANGE unify loading schemas and do not duplicate code

Fixes #414
diff --git a/src/context.c b/src/context.c
index 86296d3..a4ac25e 100644
--- a/src/context.c
+++ b/src/context.c
@@ -747,7 +747,7 @@
         if (module) {
             mod = (struct lys_module *)lys_sub_parse_mem(module, module_data, format, unres);
         } else {
-            mod = (struct lys_module *)lys_parse_mem_(ctx, module_data, format, 0, implement);
+            mod = (struct lys_module *)lys_parse_mem_(ctx, module_data, format, NULL, 0, implement);
         }
 
         if (module_data_free) {