VS: Restore support for two-part default toolset version
Since !7637 (merged), if a two-part toolset version is requested, we fail early if globbing finds no auxiliary toolsets with that version. This broke our existing support for detecting when the default toolset matches the two-part version requested. Fix the logic to ignore the two-part globbing results if they are empty so we fall through to checking the default version.
Fixes: #24107 (closed)
Backport: release