cubicweb-vcwiki #3763176 Improve the message displayed when computed diff is empty [validation pending]

... in the historic form. As of now a message like "could not compute diff" is displayed.

prioritynormal
typeenhancement
done in0.2.0
load0.100
load left0.000
closed by#cbcaac873304 [history] Improve the message displayed when the diff between to revisions is empty.
patch[history] Improve the message displayed when the diff between to revisions is empty. [applied]