der: return `Tag::Integer.length_error()` on empty ints #2994

Job	Run time
build (1.72.0, thumbv7em-none-eabi)	51s
minimal-versions	0s
build (1.72.0, wasm32-unknown-unknown)	53s
build (stable, thumbv7em-none-eabi)	51s
test (1.72.0)	3m 36s
build (stable, wasm32-unknown-unknown)	53s
test (stable)	3m 32s
	10m 36s

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