path_parser: When reading a number, don't call powf() if there's no exponent
path_parser: When reading a number, don't call powf() if there's no exponent

powf() was showing up in the profile.  We'll switch to Rust's own
number reader later, but for that we have to change the parsing
machinery to be able to slice the original string.

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg