cubicweb #3932503 exception handling in AjaxController shadows hides exception content [validation pending]

If an ajaxfunc decorated function raises an exception other than a hand-made RemoteCallFailed exception, then the reason of the returned JSON dictionary is hopelessly empty.

prioritynormal
typebug
done in3.18.6
load0.500
load left0.000
closed by#8227358aa983 [web] Return useful error messages when exceptions arise in ajax controllers (closes #3932503)
patch[web] Return useful error messages when exceptions arise in ajax controllers (closes #3932503) [applied]