Carbon crash on code snippet with redefined variable

Description of the bug:

Crashed when I accidentally duplicated a line and ended up defining a variable twice, once bound and once unformed.

What did you do, or what's a simple way to reproduce the bug?

https://carbon.compiler-explorer.com/z/5PaTTeacs

What did you expect to happen?

Warn me I was redefining my variable

What actually happened?

Compiler crash

Any other information, logs, or outputs that you want to share?

package Test;
// Starting new example file
// Carbon

// A quick class for discussion
class AClassType {
  fn Make() -> AClassType {
    return {};
  }
};

var some_object_defined_earlier: AClassType = AClassType.Make();

var some_object_defined_earlier = AClassType;