[clang] [clang] AST Visitor: skip empty qualifiers in QualifiedTemplateName (PR #93926)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

> Even with this fix, I'm seeing a segfault in clang/lib/AST/QualTypeNames.cpp at line 216.
> I have a fix in testing that adds this check, but if you would double check it after it goes in, that would be helpful.
> 
> Unfortunately the failure is in an internal tool, against internal sources, which makes getting a reproducer a long process. I'm also working on that.

The fix gets the intended behavior right.

There are `unittests` for QualTypeNames, a new test case could go in there.

https://github.com/llvm/llvm-project/pull/93926