On open repository open common cat file batch and batch-check (#15667)

Use common git cat-file --batch and git cat-file --batch-check to
significantly reduce calls to git.
    
Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/git/repo_branch_nogogit.go

@@ -13,12 +13,30 @@ import (
 	"strings"
 )
 
+// IsReferenceExist returns true if given reference exists in the repository.
+func (repo *Repository) IsReferenceExist(name string) bool {
+	if name == "" {
+		return false
+	}
+
+	wr, rd, cancel := repo.CatFileBatchCheck()
+	defer cancel()
+	_, err := wr.Write([]byte(name + "\n"))
+	if err != nil {
+		log("Error writing to CatFileBatchCheck %v", err)
+		return false
+	}
+	_, _, _, err = ReadBatchLine(rd)
+	return err == nil
+}
+
 // IsBranchExist returns true if given branch exists in current repository.
 func (repo *Repository) IsBranchExist(name string) bool {
 	if name == "" {
 		return false
 	}
-	return IsReferenceExist(repo.Path, BranchPrefix+name)
+
+	return repo.IsReferenceExist(BranchPrefix + name)
 }
 
 // GetBranches returns branches from the repository, skipping skip initial branches and