pp_ctl.c:pp_flop: Avoid redundant SvNV calls

Calling SvNV on an SV that is IOK is unnecessary, and results in an
extra function call if the SV is not NOKp.  If an NV is out of range
and has been used as an int, it will be IOKp but not IOK.
Merge branch 'blead' of github.com:wolfsage/perl-1 into blead