Fixed an issue with how the let expression branches interact with branches in selects and ifs.
Fixed an issue with how the let expression branches interact with branches in selects and ifs.


Former-commit-id: 9dd08859a08303031be29f6cb3f571223f521c67
darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide