Fix thread unsafe code in SnackbarMessageQueue. (#1874)
Fix thread unsafe code in SnackbarMessageQueue. (#1874)

* Fix thread unsafe code in SnackbarMessageQueue.

* Formatting

Added braces for lock statements

Co-authored-by: Kevin Bost <18855cb1058909111024f7369a548b13622a3903@gmail.com>
ButchersBoy/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit