[FIX] avoid overwriting sensible error message with garbage when reading or decoding the CSV file fails

also improve error message in case of decoding error (turns out UnicodeDecodeError has everything you need to know exactly what blew up, who knew?)

bzr revid: xmo@openerp.com-20121104192508-62gnf3syv59am4ki

addons/web/controllers/main.py

@@ -1953,13 +1953,15 @@ class Import(View):
                 # filtering in case of e.g. o2m content rows)
                 if any(row)
             ]
-        except UnicodeDecodeError:
-            error = u"Failed to decode CSV file using encoding %s" % csvcode
+        except UnicodeDecodeError, e:
+            # decode with iso-8859-1 for error display: always works-ish
+            error = u"Failed to decode cell %r using encoding %s: '%s'" % (
+                e.object, e.encoding, e.reason)
         except csv.Error, e:
             error = u"Could not process CSV file: %s" % e
 
-        # If the file contains nothing,
-        if not data:
+        # If the file contains nothing, and the import has not already blown up
+        if not (error or data):
             error = u"File to import is empty"
         if error:
             return '<script>window.top.%s(%s);</script>' % (