1.50.3-1.51.1: add with no journal and no options gives an error, should pick default path

[simonmichael]

In hledger 1.50.3-1.51.1, when LEDGER_FILE is unset and ~/.hledger.journal does not exist, hledger add fails instead of creating that file. This is more fallout from the recent include/glob changes.

~$ HOME=/tmp LEDGER_FILE= hledger add
hledger: Error: neither LEDGER_FILE nor "/tmp/.hledger.journal" was found