[clang] [clang-repl] Keep the first llvm::Module empty to avoid invalid memory access. (PR #89031)

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

> If there's a trivial reproducer for the original issue it may be worth adding it as a regression test.

It is manifested in https://github.com/llvm/llvm-project/pull/84758 which has a test. That PR will unblock the other one which will make the test more explicit by changing the valgrind invalid memory access into a proper crash.

https://github.com/llvm/llvm-project/pull/89031