/damage can provide fewer variables to death message than expected, printing unformatted message

The bug:

Some damage type death messages expect two variables for the translation: one for the victim and one for the killer. In vanilla, this always works fine, but with /damage, it's possible to deal damage of this type without a killer. In this case, due to the recent changes to out of bounds variables, the message is printed without any variable substitution.

How to reproduce:

/damage @s 30 fireball

• Prints "%1$s was fireballed by %2$s"

Expected result:

• The message should output either: "[username] was fireballed by a command" or "[username] was fireballed by %2$s"