[clang] [clang-repl] fix segfault in CleanUpPTU() (PR #75629)

[Pavel Kalugin via cfe-commits]

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@@ -0,0 +1,10 @@
+// RUN: clang-repl "int x = 10;" "{ int t; a::b(t); }" "int y = 10;"
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p4vook wrote:

I don't quite understand, the `code-undo.cpp` doesn't seem to have anything that produces an error, but this test does.
If we define a::b(t), clang-repl stops segfaulting.

https://github.com/llvm/llvm-project/pull/75629