Avoid a crash when entering invalid dates (e.g., enter "111" for a transaction date).
gnc_parse_date is ignoring the return code from qof_scan_date which causes it to
send uninitialized values to gnc_mktime which crashes if the date is too ridiculous.
Presumably this worked before because mktime took anything without crashing.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@22755 57a11ea4-9604-0410-9ed3-97b8803252fd