Default number of rows in Differences visualizer does not seem to work/match documentation

[gwhitney]

The "description" of the "Number of rows" parameter to the Differences visualizer states: "If zero, defaults to the length of top row". However, entering 0 results in an error message "Number of rows must be positive", and leaving it blank appears to default to the particular value 5, regardless of the length of the top row. The description and actual behavior should be chosen rationally and synchronized.

[gwhitney]

This appears to be working in ui2 now, presumably thanks to #420. The "Number of rows" parameter has no description, but starts empty with a greyed-out 12 in it, and indeed, shows 12 rows. Typing in a 0 results in the error message "Need at least one row" and any positive value produces the corresponding number of rows. Deleting the entry reverts to a greyed-out 12 and 12 rows shown. As all seems well, closing.