It should use the destination type and not the source type to check if
the conversion would be to a value that's in range.
NOTE: A finite f64 value that is larger than the f32 value range now produces
None when converted to f32 with ToPrimitive.
Previously, too large f64 values would produce inf f32 values. This `as`
cast has an undefined result and was not specified to always produce for
example `inf`.
The conversion preserves nan/+-inf specifically.
bluss
Łukasz Jan Niemier