Better error message for bad elem_size field.
Better error message for bad elem_size field.


Former-commit-id: af3360a05da3acf9fa22540f9b51820f6690b0e7
Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide