ZeroDivisionError on amount parsing

[hsoft]

@@@
Application Identifier: com.hardcoded_software.moneyguru
Application Version: 2.3.3

Traceback (most recent call last):
File "hscommon/cocoa/inter.pyc", line 140, in setValue_forColumn_row_
File "hsgui/table.pyc", line 333, in set_cell_value
File "core/gui/transaction_table.pyc", line 225, in amount
File "core/app.pyc", line 123, in parse_amount
File "core/model/amount.pyc", line 101, in parse_amount
File "", line 1, in
ZeroDivisionError: int division or modulo by zero
@@@

To reproduce, simply enter something like "42/0" in an amount field.

[hsoft]

(from [3ead1b84ba5b]) [#229 state:fixed] Fix crash on zero division expression in amount.
https://bitbucket.org/hsoft/moneyguru/changeset/3ead1b84ba5b/