Fix interactive-graph / Interactive2.MovableLine
Fix interactive-graph / Interactive2.MovableLine

Summary:
Turns out we needed that if check around this.movable :).
I should have tested that.

Test Plan:
 * load test.html
 * add an interactive-graph
 * assert there were no js errors

Auditors: justinjaffray

learningequality/perseus,chirilo/perseus,abe4mvp/perseus,alexristich/perseus,huangins/perseus,sachgits/perseus,ariabuckles/perseus,junyiacademy/perseus,learningequality/perseus,daukantas/perseus,iamchenxin/perseus,huangins/perseus,ariabuckles/perseus,daukantas/perseus,chirilo/perseus,ariabuckles/perseus,ariabuckles/perseus,junyiacademy/perseus,iamchenxin/perseus,alexristich/perseus,abe4mvp/perseus,sachgits/perseus