Ensure that GitRepo is set on Empty repositories (#8539)

Both issues/new and settings/hooks/git expect `ctx.Repo.GitRepo` to be set.
This PR changes the context code to open the GitRepo.

Fixes #8538

modules/context/repo.go

 			}
 		}
 
-		// repo is empty and display enable
-		if ctx.Repo.Repository.IsEmpty || ctx.Repo.Repository.IsBeingCreated() {
+		// Disable everything when the repo is being created
+		if ctx.Repo.Repository.IsBeingCreated() {
 			ctx.Data["BranchName"] = ctx.Repo.Repository.DefaultBranch
 			return
 		}
 		}
 		ctx.Repo.GitRepo = gitRepo
 
+		// Stop at this point when the repo is empty.
+		if ctx.Repo.Repository.IsEmpty {
+			ctx.Data["BranchName"] = ctx.Repo.Repository.DefaultBranch
+			return
+		}
+
 		tags, err := ctx.Repo.GitRepo.GetTags()
 		if err != nil {
 			ctx.ServerError("GetTags", err)