Bugfix on _resize when using BC Math and on some locales (as french)

Similar to #1571.

bcdiv use string parameters (http://php.net/manual/en/function.bcdiv.php), so the float conversion seems useless (since it has already been converted to a string by convert_number).

And on some locales, 2.3 will be converted to "2,3" instead of "2.3" when converting float to string, and bcdiv doesn't support that (always returning 0).

Thanks,