Fix BEAM process crash on nested empty map property enumeration

[andr-ec]

Fixes #7

beam_proxy.get_own_property_names calls js_malloc(ctx, 0) when the BEAM map is empty and has no overrides, hitting QuickJS's assert(size != 0). Return early with empty results when total == 0.

Change

lib/quickbeam/beam_proxy.zig — 4 lines added:

const total = map_size + override_count;
if (total == 0) {
    ptab.* = null;
    plen.* = 0;
    return 0;
}

Test

test/core/beam_proxy_empty_map_test.exs — 3 cases: Object.keys, for...in on nested empty map, plus non-empty control.

[dannote]

Thanks for the fix! Merged with one additional change on top: convertValue now also skips proxy creation for empty maps (matching the existing guard in beam_to_js.convert_map), so they never become proxies in the first place. Your defensive check in get_own_property_names is kept as a belt-and-suspenders guard.