runtime: don't re-initialize itab while looking for missing function
The itab we're initializing again, just to figure out which method
is missing, might be stored in read-only memory.
This can only happen in certain weird generics situations, so it is
pretty rare, but it causes a runtime crash when it does happen.
Fixes #65962
Change-Id: Ia86e216fe33950a794ad8e475e76317f799e9136
Reviewed-on: https://go-review.googlesource.com/c/go/+/567615 Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@google.com>