Segfault during glyph outlining about freetype-rs

[johnoneil]

Yeah I'm seeing this as well.
The origin of the issue (at least for me) seems to be in attempting to get an outline for a glyph with no geometry (say for example a space).
This case can be reproduced via the glyph_outline example without changes via:

cargo run --example glyph_outline examples/assets/FiraSans-Regular.ttf ' '

Here I'm passing a space as the outlined character (unicode codepoint 0x20 or 32 decimal).

I've caught this in the debugger and it appears a null ptr check is needed in the following code in outline.rs

impl<'a> Iterator for ContourIterator<'a> {
    type Item = CurveIterator<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.contour_end_idx > self.last_end_idx {
            None
        } else {
            unsafe {
                let contour_end = *self.contour_end_idx; // <-- dereferncing a null ptr here !!!
                let curves = CurveIterator::from_raw(self.outline, self.contour_start as isize,
                                                     contour_end as isize);
                self.contour_start = contour_end + 1;
                self.contour_end_idx = self.contour_end_idx.offset(1);

                Some(curves)
            }
        }
    }
}

I could provide a PR for this as it would improve out client which is using this crate, but as you know the binding better I'll accept how you want to proceed on this.