ProcessTextCommand_If checks attribute exists
ProcessTextCommand_If checks attribute exists

Added a check in ProcessTextCommand_If that tests if an attribute exists.
This may slightly change the original behaviour. These example illustrate.

// everything fine
Well {if game.notset:Notset has been set}.
old --> Well.
new --> Well.

// attribute does not exist
Well {if game.notset=5:Notset has been set}.
old --> error
new --> Well {if game.notset=5:Notset has been set}.

Well {if game.notset=true:Notset has been set}.
old --> ???
new --> Well {if game.notset=5:Notset has been set}.
textadventures/quest,textadventures/quest,textadventures/quest,textadventures/quest