fix(github): fall through to commit author lookup when user search returns no results

resolveAuthorInfo was returning early with an empty login when the GitHub user
search yielded zero items, so the commit-based fallback never ran. Invert the
condition to only set the login when results are present and always continue to
the next lookup strategy.

Author: luxass

src/core/github.ts

@@ -371,11 +371,9 @@ export class GitHubClient {
         items?: Array<{ login: string }>;
       }>(`/search/users?q=${q}`);
 
-      if (!data.items || data.items.length === 0) {
-        return info;
+      if (data.items && data.items.length > 0) {
+        info.login = data.items[0]!.login;
       }
-
-      info.login = data.items[0]!.login;
     } catch (err) {
       logger.warn(`Failed to resolve author info for email ${info.email}: ${formatUnknownError(err).message}`);
     }