"More than one account with unspecified amount" should be an input error, not an internal assertion

[hrj]

Running the following command in sbt console:

cli/run -c ../tests/errors/AssertionError/ae01.conf

gives:

[info] Internal Assertion Error (please report a bug):assertion failed: More than one account with unspecified amount: List(Post(Expenses:E01,None,None), Post(Assets:A01,None,None))
[info] java.lang.AssertionError: assertion failed: More than one account with unspecified amount: List(Post(Expenses:E01,None,None), Post(Assets:A01,None,None))
[info] 	at scala.Predef$.assert(Predef.scala:219)
[info] 	at co.uproot.abandon.Processor$.$anonfun$process$4(Process.scala:225)
[info] 	at co.uproot.abandon.Processor$.$anonfun$process$4$adapted(Process.scala:220)
[info] 	at scala.collection.immutable.List.foreach(List.scala:378)
[info] 	at co.uproot.abandon.Processor$.process(Process.scala:220)
[info] 	at co.uproot.abandon.CLIApp$.runApp(App.scala:187)
[info] 	at co.uproot.abandon.CLIApp$.run(App.scala:263)
[info] 	at co.uproot.abandon.CLIApp$.mainStatus(App.scala:273)
[info] 	at co.uproot.abandon.CLIApp$.main(App.scala:313)
[info] 	at co.uproot.abandon.CLIApp.main(App.scala)

This should be an input error presented nicely to the user, not an internal assertion failure.