fix: parse decimals without whole portion

[jrick]

When an transaction entry contains a decimal amount with no whole portion specified, assume the whole part is zero.

This avoids creating additional accounts from misparsed transactions, where the account name otherwise contained the decimal portion at the end.

[howeyc]

I'm good with the change, but what about something like "-.34", should that be handled?

[jrick]

Yes, that seems reasonable as well.