Background library loading threads call GetRow() through
loadFromScope(), which writes to m_rowCache concurrently
with the main thread clearing it in loadTables(). The
unsynchronized access corrupts the map's red-black tree,
causing a double-free crash when switching projects.
Add m_rowCacheMutex to protect all m_rowCache accesses.
Also replace std::tie with std::make_tuple to avoid
unnecessary temporary conversions, and use a single
find() instead of contains() followed by at().
Seth Hillbrand
e60e619655