Automatic locale results in blank page for unimplemented language

[j123b567]

When the default locale is automatic, but the client locale is not implemented (e.g. "cs"), client script fails and no page is displayed.

Deeper investigation:
oui-ui-core/vue/src/App.vue calls rpc function oui.load_locales

For unknown locale, oui-httpd/files/rpc/oui.lua:load_locales returns empty Lua object {}

This object is later identified as an object and not as an array by oui-httpd/src/lua2json.c:lua_test_array, because it is empty.

RPC then returns JSON result {} instead of []

In oui-ui-core/vue/src/App.vue, on result, method forEach is called, which does not exists for object type, but exists for array type. This causes Uncaught (in promise) TypeError: t.forEach is not a function javascript exception and client side javascript completely terminates.

I would like to fix it myself, but I don't know the best place to do it.
Doing the similar trick like mpx/lua-cjson@3b1429f would be nice but my knowledge of Lua is limited to create a PR. Other solutions are probably easier, but ugly (test special case of {} in Vue, etc.)

[zhaojh329]

This is the tricky question of whether to turn to "{ }" or "[ ]" for an empty Lua Table.

[zhaojh329]

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