Fix error with file size check with submodules

Closes #152

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
-v 8.3.0 (unreleased)
-  - Merge when build succeeds (Zeger-Jan van de Weg)
 v 8.4.0 (unreleased)
+  - Fix error with file size check with submodules (Stan Hu)
   - Implement new UI for group page
   - Implement search inside emoji picker
   - Add API support for looking up a user by username (Stan Hu)

lib/gitlab/git_access.rb

@@ -257,7 +257,7 @@ module Gitlab
           next if diff.deleted_file
 
           blob = project.repository.blob_at(commit.id, diff.new_path)
-          if blob.size > git_hook.max_file_size.megabytes
+          if blob && blob.size && blob.size > git_hook.max_file_size.megabytes
             return build_status_object(false, "File #{diff.new_path.inspect} is larger than the allowed size of #{git_hook.max_file_size} MB")
           end
         end

spec/lib/gitlab/git_access_spec.rb

@@ -311,6 +311,13 @@ describe Gitlab::GitAccess, lib: true do
         project.git_hook.update(max_file_size: 2)
         expect(access.git_hook_check(user, project, 'refs/heads/master', 'cfe32cf61b73a0d5e9f13e774abde7ff789b1660', '913c66a37b4a45b9769037c55c2d238bd0942d2e')).to be_allowed
       end
+
+      it "returns true when size is nil" do
+        allow_any_instance_of(Gitlab::Git::Blob).to receive(:size).and_return(nil)
+        project.create_git_hook
+        project.git_hook.update(max_file_size: 2)
+        expect(access.git_hook_check(user, project, 'refs/heads/master', 'cfe32cf61b73a0d5e9f13e774abde7ff789b1660', '913c66a37b4a45b9769037c55c2d238bd0942d2e')).to be_allowed
+      end
     end
   end
 end