[widgets][experimenteditor IOMapping through rowCount and not element count

Fixes #257
4 jobs for 257_experiment_editor_io_number_bug in 16 minutes and 9 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Build
passed #199805
docker
build_linux_36

00:06:34

90.0%
passed #199806
docker
build_linux_37

00:06:24

90.0%
passed #199803
macosx
build_macosx_36

00:16:09

90.0%
passed #199804
macosx
build_macosx_37

00:15:52

90.0%