Returns a non-zero number if the specified label exists in the current scope.
Boolean := IsLabel(LabelName)
Type: Integer (boolean)
This function returns 1 (true) if the specified label exists within the current scope, otherwise 0 (false).
This function is useful to avoid runtime errors when specifying a dynamic label for Goto.
When called from inside a function, only that function's labels are searched. Global labels are not valid targets for a local goto.