Expose argCount and isNull in Function.Args

[angusholder]

SQLite allows defining functions to have any number of arguments, by passing in numArgs = -1 when defining the function, then when called asking how many arguments were passed in.

There's also currently no easy way to check if an argument is null if it's an int/long/double, you have to resort to calling getString/getBlob and checking if their result is null.

Do you consider the SQLiteDatabase.Function.Args interface to be stable, or would it be possible to add two new methods to it to expose this functionality?