convert_wycheproof: Return an error instead of panicking

This way we get the context and debugging is a bit easier. In principle
this should be unreachable because there is a documented set of possible
closed types. However, we're missing a few and it's easier to debug if
we can see the offending file.

Change-Id: I33494da50b3a9ebe337d446eb2cf0a93e7dda063
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/91767
Reviewed-by: Xiangfei Ding <xfding@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
Presubmit-BoringSSL-Verified: Boringssl LUCI CQ <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com>
Commit-Queue: Xiangfei Ding <xfding@google.com>

util/convert_wycheproof/convert_wycheproof.go

diff --git a/util/convert_wycheproof/convert_wycheproof.go b/util/convert_wycheproof/convert_wycheproof.go
index 6125275..bf435b9 100644
--- a/util/convert_wycheproof/convert_wycheproof.go
+++ b/util/convert_wycheproof/convert_wycheproof.go
@@ -79,7 +79,7 @@
 			}
 		}
 	default:
-		panic(fmt.Sprintf("Unknown type for %q: %T", key, valueAny))
+		return fmt.Errorf("Unknown type for %q: %T", key, valueAny)
 	}
 	return nil
 }