1.31.1 cpptools.exe gets stuck if C/C++ DevTools invokes workspace symbol after the database is reset

[sean-mcmanus]

1. Do a Reset Database (it might also repro with a new project with no database, not sure).
2. With the C/C++ DevTools extension installed with "cpp-devtools.enableCppCodeEditingTools": true use a query like how many references to mySymbol are there? #GetSymbolReferences_CppTools.

Bug: cpptools.exe can get permanently stuck if the getWorkspaceSymbol occurs while after the database reset and the database is still empty.

Doesn't repro with 1.31.0 or earlier.

It seems to require workspace symbols to be invoked by DevTools and not user invoked, maybe because the user invoked method triggers a cancel if the UI is abandoned.