Fix type-checking of select to handle non-concrete condition type

Testing SROA I discovered that the current type-checking procedure for ternary nodes fails to type-check select if the condition's type is not concrete yet. For example, on main the new example products.hir fails to compile with

cargo run --bin hercules_driver -- hercules_samples/products.hir "SROA Xdot(true)"

(though if the passes are only Xdot(true) type-checking succeeds).