Breaks when pressing <delete> on empty query

[pmf-ids]

When calling jiq with

echo 1 | jiq

it opens up fine, displaying

[jq]> .

1

with the cursor being next to the dot. Hitting backspace removes the dot (which is expected behaviour). Hitting backspace again does nothing (also as expected). Now, hitting delete makes jiq crash with the message

panic: runtime error: slice bounds out of range [1:0]

goroutine 1 [running]:
github.com/fiatjaf/jiq.(*Query).Delete(0xc0002a6030, 0x0, 0x0, 0x0, 0x0)
	/home/fiatjaf/comp/jiq/query.go:58 +0x238
github.com/fiatjaf/jiq.(*Engine).Run(0xc0002d2000, 0x0)
	/home/fiatjaf/comp/jiq/engine.go:126 +0xaa8
main.run(0xc0002d2000, 0xc0002a6000, 0xc00028c1f0)
	/home/fiatjaf/comp/jiq/cmd/jiq/jiq.go:59 +0x32
main.main()
	/home/fiatjaf/comp/jiq/cmd/jiq/jiq.go:55 +0x18d

This does not happen when hitting delete while the dot (or any other filter) is still visible.

Tested on jiq version 0.7.1-3-g5dec899