cubicweb-forge #2896216 do not silently ignore unknown icon image format [validation pending]

prioritynormal
typebug
done in1.9.2
load0.250
load left0.000
closed by#cb60cffa6771 [hooks] properly raise a ValueError on unhandled icon format (closes #2896216)
patch[hooks] properly raise a ValueError on unhandled icon format (closes #2896216) [applied]