Fix crash on passing false as value in table to table.copy(t)

[est31]

Fixes #2293.

[est31]

changed commit message so that nobody thinks this now allows table.copy(false).

[ShadowNinja]

• copyiftable -> copy_if_table -> copy_val
• Missing space after comma in second call to ^.
• Function format is [local ]function x(), not [local ]x = function()
• Maybe the helper function should be inlined.
• Local functions are not global by definition, the do end is unnecessary.

[est31]

This method also works, and doesn't need a helper function.

[ShadowNinja]

👍 (although I'd remove the superfluous parenthesis)

[Zeno-]

commit 7c5accf

Also added to freeze branch: commit 61588a4