stage2: fix bug where invalid ZIR was generated

The following code caused an assertion to be hit:
```
pub fn main() void {
    var e: anyerror!c_int = error.Foo;
    const i = e catch 69;
    assert(69 - i == 0);
}
```
a483e38df6Timon Kruiper committed on 4/8/2021, 12:23:18 PMparentac14b52
1 file changedLine totals unavailable