der: return `Tag::Integer.length_error()` on empty ints #2921

Job	Run time
build (1.72.0, thumbv7em-none-eabi)	37s
minimal-versions	0s
build (1.72.0, wasm32-unknown-unknown)	38s
build (stable, thumbv7em-none-eabi)	38s
test (1.72.0)	1m 55s
build (stable, wasm32-unknown-unknown)	41s
test (stable)	1m 41s
	6m 10s

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