types.is_empty fails for tables with boolean keys

[ethernidee]

if o == nil or (type(o) == "table" and not next(o))

not next(o) should be probably replaced with next(o) == nil, because it's valid to store FALSE as table key. If FALSE is returned as first key, the check will treat table as empty. The order of key traversals is undefined, thus types.is_empty can produce random bugs.

Proof:
types.is_empty({ [false] = 777 }) -- true

[mpeterv]

Fixed.