This default-zero allowed the bug introduced in
68b47307b4 (and fixed in
4c371734b5) not to generate a compiler
warning for `-Wuninitialized`, since it was initialized to `0`.
However, `0` is not a correct starting value for this variable. Remove
the initialization and require every code path to assign a meaningful
value.
Switch to use `std::in_range` to validate that no truncation occurs, and
trust that the compiler will optimize this out when the type passed to
`std::in_range` can represent all values that the argument can
represent.
03cedbb4cc