Fix float round/2, floor/2, ceil/2 raises wrong exception for invalid precision

[AlexGx]

Fixes Float.round/2, Float.floor/2, Float.ceil/2 raises wrong exception for invalid precision

iex> Float.round(1.1, %{})
** (Protocol.UndefinedError) protocol String.Chars not implemented for Map

expected:

** (ArgumentError) precision %{} is out of valid range of 0..15

I did not add tests because similar tests for other methods were recently removed during "warnings when running tests" cleanup.

[josevalim]

Instead of changing this here, let's add guards around the precision in the callers to this function.

[AlexGx]

All of them were already using guards. if remove the fallback clause, the error changes from ArgumentError to FunctionClauseError. Did I understand you correctly?

...
@precision_range 0..15
...

  def round(float, precision) when is_float(float) and precision in @precision_range do
    round(float, precision, :half_up)
  end

  def round(float, precision) when is_float(float) do
    raise ArgumentError, invalid_precision_message(precision)
  end

[josevalim]

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