Fix a regression in the semantics of `Form.errors`; It should be an empty dict when there are no errors, not a dict of field names with empty lists. Thanks moraes.
Fix a regression in the semantics of `Form.errors`; It should be an empty dict when there are no errors, not a dict of field names with empty lists. Thanks moraes.

hsum/wtforms,pawl/wtforms,skytreader/wtforms,pawl/wtforms,jmagnusson/wtforms,Aaron1992/wtforms,Xender/wtforms,cklein/wtforms,Aaron1992/wtforms,wtforms/wtforms,crast/wtforms,subyraman/wtforms