[Clang] Fix a crash when recursively callig a default member initializer.

This fixes a regression introduced by ca619613, that would lead
to a segfault due to stack exhaustion when recursively calling
a default member initializer.

Fixes #60082

I'm not able to  get clang to emit a stack exhaustion warning,
which it seems like it should be able to.

Reviewed By: shafik

Differential Revision: https://reviews.llvm.org/D142401