Fixed an issue in the block flattening visitor that was not handling recusrion correctly.
Fixed an issue in the block flattening visitor that was not handling recusrion correctly.


Former-commit-id: e8a3788a058b6ab9108070afc569e13752f1a6f4
darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide