[web2py] csv import crashes on GAE

[Bas Ti]

importing a csv on GAE (including image blobs) fails on GAE:

Traceback (most recent call last):
  File 
"/base/data/home/apps/s~cambeoserver/1.364313602794800132/gluon/restricted.py", 
line 212, in restricted
    exec ccode in environment
  File 
"/base/data/home/apps/s~cambeoserver/1.364313602794800132/applications/Cambeo/controllers/appadmin.py",
 line 450, in <module>
  File 
"/base/data/home/apps/s~cambeoserver/1.364313602794800132/gluon/globals.py", 
line 193, in <lambda>
    self._caller = lambda f: f()
  File 
"/base/data/home/apps/s~cambeoserver/1.364313602794800132/gluon/tools.py", line 
2929, in f
    return action(*a, **b)
  File 
"/base/data/home/apps/s~cambeoserver/1.364313602794800132/applications/Cambeo/controllers/appadmin.py",
 line 257, in select
    tb = tb,
UnboundLocalError: local variable 'tb' referenced before assignment


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