When printing a check from a payment the check number wizard shows the
number 1 for the next check... it should show the last check added one
+1, it doesn't because it doesn't exclude the account.payments without
checknumber.
This fix excludes the account.payments without checknumber so that it
doesn't shows "1" as the next check number when there are multiple new
checks to be printed
X-original-commit: adfb8299141cb8fe9883741c43871a51f849655e
Andres Calle
176bf1442b