re_intuit_start(): MBOL use char for float max

re_intuit_start(): MBOL use char for float max

Do the "maximum place \n can appear within the float range" calculation
in chars rather than bytes. Doing it in bytes is logically incorrect,
although I think the worst outcome is that a string is falsely accepted
by intuit then has to be failed by a full run of the regex engine.
But I couldn't think of a test that would show a significant performance
difference.