fix(commit-model): load signature_data only if project is defined

app/models/commit.rb

@@ -122,7 +122,7 @@ def initialize(raw_commit, project)
     @project = project
     @statuses = {}
     repo = self.project.repository.raw_repository
-    @signature_data = Gitlab::Git::Commit.extract_signature_lazily(repo, self.sha || self.id)
+    @signature_data = Gitlab::Git::Commit.extract_signature_lazily(self.project.repository.raw_repository, self.sha || self.id) if project
     @gpg_commit = Gitlab::Gpg::Commit.new(self) if project
     @x509_commit = Gitlab::X509::Commit.new(self) if project
   end