[migration] fix bug in `CWAttributeAddOp.revertprecommit_event`
The `rdefdef` attribute is set during the operation execution. In some the
operation crash before this assignment. In such case `revertprecommit` raise an
attribute error crashing the whole process and shadowing the original error.
This changeset detect and Avoid this situation.
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/web usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/share/cubicweb/cubes/shared/data usr/share/cubicweb/cubes/shared
debian/tmp/usr/share/cubicweb/cubes/shared/wdoc usr/share/cubicweb/cubes/shared