Prevent 0,0,0,0 control points

[lklepner]

somehow control points of 0,0,0,0 appear occasionally which breaks the rectification in a dramatic fashion.

it would be good if we could determine how/why this was happening and prevent it and/or prevent 0,0,0,0 control points from being accepted entirely

[mgiraldo]

this is probably due to the "add gcp manually" functionality below the table which creates and saves an empty (0,0,0,0) point. maybe it should be replaced with a popup/modal dialog with the four boxes prompting the user to type the data or dismiss before creation.