Refactor git command stdio pipe (#36393)

And remove the incorrect `ensureValidGitRepository`

modules/git/gitcmd/utils.go

@@ -5,6 +5,7 @@ package gitcmd
 
 import (
 	"fmt"
+	"io"
 
 	"code.gitea.io/gitea/modules/util"
 )
@@ -18,3 +19,30 @@ func ConcatenateError(err error, stderr string) error {
 	errMsg := fmt.Sprintf("%s - %s", err.Error(), stderr)
 	return util.ErrorWrap(&runStdError{err: err, stderr: stderr, errMsg: errMsg}, "%s", errMsg)
 }
+
+func safeClosePtrCloser[T *io.ReadCloser | *io.WriteCloser](c T) {
+	switch v := any(c).(type) {
+	case *io.ReadCloser:
+		if v != nil && *v != nil {
+			_ = (*v).Close()
+		}
+	case *io.WriteCloser:
+		if v != nil && *v != nil {
+			_ = (*v).Close()
+		}
+	default:
+		panic("unsupported type")
+	}
+}
+
+func safeAssignPipe[T any](p *T, fn func() (T, error)) (bool, error) {
+	if p == nil {
+		return false, nil
+	}
+	v, err := fn()
+	if err != nil {
+		return false, err
+	}
+	*p = v
+	return true, nil
+}