fix(sem): `nimsuggest` crashing for ill-formed AST #4160

Job	Run time
Provide additional context for the workflow	9s
Build release binaries (Linux)	11m 21s
Build release binaries (macOS)	9m 19s
Build source archive	5m 25s
Build and test tooling (Linux)	4m 51s
Test the compiler and stdlib (Linux, batch #0)	9m 47s
Build docs and release artifacts (Linux)	13m 7s
Build and test tooling (macOS)	5m 10s
Test the compiler and stdlib (Linux, batch #1)	8m 45s
Build docs and release artifacts (macOS)	10m 21s
Test the compiler and stdlib (macOS, batch #0)	10m 32s
Test the compiler and stdlib (macOS, batch #1)	9m 27s
Build release artifacts from source archive (Linux)	18m 58s
Build release artifacts from source archive (macOS)	12m 46s
Test release artifacts	1m 54s
All check passed	1s
	2h 11m 53s

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