cubicweb #3289774 crash on error page generation vs some unicode characters [validation pending]

hidding the original error.

prioritynormal
typebug
done in3.17.11
load0.100
load left0.000
closed by#9d145b4c4e53 [web] make sign_text unicode aware, avoid crash with non-ascii chars. Closes #3289774
patch[web] make sign_text unicode aware, avoid crash with non-ascii chars. Closes #3289774 [applied]