[lldb] Silence warning with latest MSVC on Windows

Fixes:
```
[3465/3822] Building CXX object tools\lldb\source\Plugins\SymbolFile\CTF\CMakeFiles\lldbPluginSymbolFileCTF.dir\SymbolFileCTF.cpp.obj
C:\git\llvm-project\lldb\source\Plugins\SymbolFile\CTF\SymbolFileCTF.cpp(606) : warning C4715: 'lldb_private::SymbolFileCTF::CreateType': not all control paths return a value
```