panic: `key lacking binding` with fuzzed code

[correctmost]

Describe the Bug

Pyrefly crashes when checking this fuzzed code:

(a:=).:b

ERROR Thread panicked, shutting down: panicked at pyrefly/lib/binding/bindings.rs:475:13:
Internal error: key lacking binding, module=__unknown__, path=/home/user/crash.py, key=Key::Definition(a 1:2-3), key-debug=Definition(ShortIdentifier(1..2))

Version info

Reproducible with 0.64.1 and commit c2ba6d4

Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeSIAFKogLwCUhi2IANCGQE4xhSmEAXXAFsoFAMQACAAqluvUpLRY8%2BSQGNc6SAHMArp1QCIWwgB10UgMowYkgBYCBxOIgD0brjz6FcnHW4w6G6YuOpwbpraEPqGxlpukmB%2BkqgAbqjQqNiwGlq6BkYm6JK4xPHocOboZAL2WgC0aTCccMWStJJmIADMhACMAEzdFgDaLZx%2BcAC6FnroEMLEfgIwmA2YENzqxs0dkgDkMeh%2BMAcWJwIN3ACOeltrDQDWMKQNqOrq8HD7BwDuqE46HO6BAAF92B9djAAGLQGAUZQ4AgkchgoA

(Only applicable for extension issues) IDE Information

No response