Interactive2: Fix bug in ray drawing

Summary:
We missed a function rename and had a small logic bug
in the new fast ray drawing.

The function name caused rays to crash; when that was
fixed the logic bug caused rays to not have a line segment
in the middle.

Test Plan:

Load [this item](http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22%2A%2ADrag%20the%20ray%20so%20it%20has%20an%20endpoint%20at%20point%20%24%5C%5Ctext%7BA%7D%24%20and%20goes%20through%20one%20of%20the%20other%20black%20points.%20The%20ray%20should%20also%20be%20parallel%20to%20the%20pink%20line%20segment.%2A%2A%5Cn%5B%5B%E2%98%83%20interactive-graph%201%5D%5D%5Cn%5CnThis%20is%20a%20ray%20because%20it%20has%20%5B%5B%E2%98%83%20dropdown%201%5D%5D%2C%20and%20it%20continues%20forever%20in%20%5B%5B%E2%98%83%20dropdown%202%5D%5D.%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%22interactive-graph%201%22%3A%7B%22type%22%3A%22interactive-graph%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22step%22%3A%5B1%2C1%5D%2C%22backgroundImage%22%3A%7B%22url%22%3A%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F0b3e59442adc6229aae62e4f72428b0d104973bd.png%22%2C%22scale%22%3A%221%22%2C%22bottom%22%3A0%2C%22left%22%3A0%2C%22width%22%3A400%2C%22height%22%3A400%7D%2C%22markings%22%3A%22none%22%2C%22labels%22%3A%5B%22x%22%2C%22y%22%5D%2C%22showProtractor%22%3Afalse%2C%22showRuler%22%3Afalse%2C%22rulerLabel%22%3A%22%22%2C%22rulerTicks%22%3A10%2C%22range%22%3A%5B%5B-10%2C10%5D%2C%5B-10%2C10%5D%5D%2C%22gridStep%22%3A%5B1%2C1%5D%2C%22snapStep%22%3A%5B0.5%2C0.5%5D%2C%22graph%22%3A%7B%22type%22%3A%22ray%22%7D%2C%22correct%22%3A%7B%22type%22%3A%22ray%22%2C%22coords%22%3A%5B%5B2%2C8%5D%2C%5B8%2C2%5D%5D%7D%7D%2C%22version%22%3A%7B%22major%22%3A0%2C%22minor%22%3A0%7D%7D%2C%22dropdown%201%22%3A%7B%22type%22%3A%22dropdown%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22choices%22%3A%5B%7B%22content%22%3A%22zero%20endpoints%22%2C%22correct%22%3Afalse%7D%2C%7B%22content%22%3A%22one%20endpoint%22%2C%22correct%22%3Atrue%7D%2C%7B%22content%22%3A%22two%20endpoints%22%2C%22correct%22%3Afalse%7D%5D%2C%22placeholder%22%3A%22%22%7D%2C%22version%22%3A%7B%22major%22%3A0%2C%22minor%22%3A0%7D%7D%2C%22dropdown%202%22%3A%7B%22type%22%3A%22dropdown%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22choices%22%3A%5B%7B%22content%22%3A%22zero%20directions%22%2C%22correct%22%3Afalse%7D%2C%7B%22content%22%3A%22one%20direction%22%2C%22correct%22%3Atrue%7D%2C%7B%22content%22%3A%22two%20directions%22%2C%22correct%22%3Afalse%7D%5D%2C%22placeholder%22%3A%22%22%7D%2C%22version%22%3A%7B%22major%22%3A0%2C%22minor%22%3A0%7D%7D%7D%7D%2C%22answerArea%22%3A%7B%22type%22%3A%22multiple%22%2C%22options%22%3A%7B%22content%22%3A%22%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%7D%7D%2C%22calculator%22%3Afalse%7D%2C%22itemDataVersion%22%3A%7B%22major%22%3A0%2C%22minor%22%3A1%7D%2C%22hints%22%3A%5B%7B%22content%22%3A%22%21%5B%5D%28https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2Fa8bfd3e9c3fed8e38dfca694bf63fbcef8fd2587.png%29%20%20%5CnHere%20are%20all%20of%20the%20possible%20rays%20that%20come%20from%20point%20%24%5C%5Ctext%7BA%7D%24%20and%20go%20through%20one%20of%20the%20other%20black%20points.%20Which%20of%20these%20is%20parallel%20to%20the%20pink%20line%20segment%3F%22%2C%22images%22%3A%7B%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2Fa8bfd3e9c3fed8e38dfca694bf63fbcef8fd2587.png%22%3A%7B%22width%22%3A400%2C%22height%22%3A400%7D%7D%2C%22widgets%22%3A%7B%7D%7D%2C%7B%22content%22%3A%22%21%5B%5D%28https%3A%2F%2Fka-perseus-images.s3.amazonaws.com%2F602a2269ebfde56a4d875b36f4128bb282add885.png%29%22%2C%22images%22%3A%7B%22https%3A%2F%2Fka-perseus-images.s3.amazonaws.com%2F602a2269ebfde56a4d875b36f4128bb282add885.png%22%3A%7B%22width%22%3A388%2C%22height%22%3A402%7D%7D%2C%22widgets%22%3A%7B%7D%7D%2C%7B%22content%22%3A%22This%20is%20a%20ray%20because%20it%20has%20one%20endpoint%2C%20and%20it%20continues%20forever%20in%20one%20direction.%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%7D%7D%5D%7D)

See it not crash!

Celebrate!

Auditors: charlie, emily