Fix memory leak in mlt_repository

As reported here:
mltframework#961

src/framework/mlt_repository.c

@@ -339,6 +339,7 @@ void mlt_repository_close(mlt_repository self)
     mlt_properties_close(self->consumers);
     mlt_properties_close(self->filters);
     mlt_properties_close(self->producers);
+    mlt_properties_close(self->links);
     mlt_properties_close(self->transitions);
     mlt_properties_close(&self->parent);
     free(self);