gparam: fix memory leak in g_param_value_defaults()
gparam: fix memory leak in g_param_value_defaults()

We cannot  just call

    G_PARAM_SPEC_GET_CLASS (pspec)->value_set_default (pspec, &dflt_value);

without initializing the GValue first. It would call
param_string_set_default(), which would set the pointer value
to a cloned string (which later never gets released, because
the GValue is not known to hold a string).

Fixes: 6ad799ac677ae241da8b32ecf33b5cc9dc1d30bc

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib