Ensure all bound ImageParams have non-NULL host/dev pointers
Ensure all bound ImageParams have non-NULL host/dev pointers

This adds a layer of paranoia to catch failed allocations of Buffers.


Former-commit-id: 19360a7462e713aef3287652b4cf6bee3f3a1cea
darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide