Discarding a new record triggers the 'history_back' action. This makes
sense if the record was discarded from a normal form view, but not so
much when in a modal, where the expected behaviour is to close the
dialog.
This commit overrides the function in the action manager which handles
the switch to the previous view. It checks whether a dialog window is
open, in which case it simply closes it.
note: 10.0 backport from 11.0 33aa89edcloses#20405
opw-786866
closes#21792
Nicolas Lempereur
1ce4f15c39