Synchronizes the values of the parameters in this with the values at the
row is not a valid row, then the returned value is
false, and the "current-row" property is set to -1 (which means
that is_valid would return
false), with the exception that
row is -1, then the returned value is
This function can return
false if it was not allowed to be moved (as it emits the "validate-set" signal before being moved).
When this function returns
true, then this has actually been moved to the next row, but some
values may not have been read correctly in the row, in which case the correcsponding Holder
will be left invalid.
a DataModelIter object
the row to set this to