Support negative strides in vector->scalar condition rule.
Support negative strides in vector->scalar condition rule.


Former-commit-id: 7ec0c0701c09f2961bd7e780739abc86bc18f0cd
Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide