Fix ALoc exception in `flow.js`
Fix ALoc exception in `flow.js`

Summary:
{D16469791} broke `flow.js`. This is a workaround.

I think the code in `merge_js.ml` should be cleaned up to only use abstract locations when they're turned on, but I'll leave that for Nat or Daniel.

Reviewed By: jbrown215

Differential Revision: D16622993

fbshipit-source-id: ec1939a03dbcf3a24761ea01ac84a949f8f967fe

gabelevi/flow,mroch/flow,gabelevi/flow,gabelevi/flow,facebook/flow,mroch/flow,mroch/flow,facebook/flow,facebook/flow,samwgoldman/flow,mroch/flow,mroch/flow,facebook/flow,samwgoldman/flow,gabelevi/flow,mroch/flow,samwgoldman/flow,facebook/flow,samwgoldman/flow,gabelevi/flow,gabelevi/flow,mroch/flow,samwgoldman/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,gabelevi/flow,facebook/flow