Robustify (&fix) error throwing on APPEND
Robustify (&fix) error throwing on APPEND

If APPEND raises abort(), the (typ, dat) variables will not be set, so
we should not be using it for the  OfflineImapError Exception
string. Fixing and prettifying the string formatting a bit at the same
time.

Signed-off-by: Sebastian Spaeth <98dcb2717ddae152d5b359c6ea97e4fe34a29d4c@SSpaeth.de>

frioux/offlineimap,frioux/offlineimap