Use binary search in t2length() and explicitly check for null and undefined in Bezier function

[Rheeseyb]

Use binary search in t2length() - proposed fix for #1

Explicitly check for null and undefined - proposed fix for #2

[Rheeseyb]

Thanks for writing this library by the way!

I haven't checked the performance impact of switching to the binary search - anecdotally the tests didn't seem to take any longer.

[coveralls]

Coverage increased (+0.01%) to 99.652% when pulling 3b00350 on momentumworks:master into 8af8f32 on rveciana:master.

[rveciana]

Thank you! I'll merge the request and then I'll try to write some tests to check it in the future