fix(pick/error): set_picker_items don't throw an error if picker is inactive

[AgatZan]

• I have read CONTRIBUTING.md
• I have read CODE_OF_CONDUCT.md

Why

Everywhere else in the entire module, MiniPick.is_picker_active is checked before the assertion section. For example:

MiniPick.set_picker_items_from_cli = function(command, opts)
  if not MiniPick.is_picker_active() then return end
  local is_valid_command = H.is_array_of(command, 'string') and #command >= 1
  if not is_valid_command then H.error('`command` should be an array of strings.') end

The alternative behavior is not described in the documentation for the method.