fix #15186, regression in if lowering

[JeffBezanson]

No description provided.

[tkelman]

Travis failure was in subarray

Exception running test subarray :
On worker 4:
LoadError: BoundsError: attempt to access (1,)
  at index [2]
 [inlined code] from ./abstractarray.jl:150
 in test_cartesian at /tmp/julia/share/julia/test/subarray.jl:96
 in runtests at /tmp/julia/share/julia/test/subarray.jl:228
 in runviews at /tmp/julia/share/julia/test/subarray.jl:249
 [inlined code] from /tmp/julia/share/julia/test/subarray.jl:326

needs a rebase?

[andreasnoack]

Okay to merge?