Removed code repetition.
Missed targeting self for ds_result->rows(::tag) also changed boolean param

The ds_result->rows(::tag) method was calling the lasso rows method instead of
the ds_result->rows(::memberstream) method. (Sometimes syntax highlighting can
be deceiving. Also should have tested both use cases)

Ke dosn't like named-parameter booleans, so preemptively made useOnCreate just
an optional parameter.