Fix an assertion failure when extract_lane is called on an expression involving interleave_vectors.
Fix an assertion failure when extract_lane is called on an expression
involving interleave_vectors.


Former-commit-id: 7e2e19b6294f38d9a8188e8decadc1ec59907baf
darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide