fix: signer fills from if unset #1895

Job	Run time
doctest	2m 27s
test stable --no-default-features	2m 24s
clippy	1m 7s
docs	55s
test stable	2m 22s
test stable --all-features	2m 37s
feature-checks	5m 49s
test nightly --no-default-features	1m 11s
no-std	29s
test nightly	1m 18s
wasm-unknown	1m 46s
test nightly --all-features	1m 51s
wasm-wasi	2m 39s
test 1.76 --no-default-features	1m 35s
test 1.76	1m 36s
cfg-check	57s
fmt	20s
	31m 23s

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