[fea-rs] Handle edge case in chain context compilation #3222

Job	Run time
Clippy lints	1m 32s
fontc tests	1m 11s
Rustfmt	1m 14s
resources/scripts/ots_test.sh	1m 5s
cargo test fea-rs	1m 0s
cargo check wasm	1m 10s
Build GS and check the result	3m 9s
fontbe tests	51s
tests other than fontbe,fontc	2m 10s
cargo check no std	1m 33s
	14m 55s

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