Only update merge_base in checker if not already merged (#10908)

Fix #10766

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

services/pull/check.go

@@ -61,7 +61,7 @@ func checkAndUpdateStatus(pr *models.PullRequest) {
 	}
 
 	if !has {
-		if err := pr.UpdateCols("merge_base", "status", "conflicted_files"); err != nil {
+		if err := pr.UpdateColsIfNotMerged("merge_base", "status", "conflicted_files"); err != nil {
 			log.Error("Update[%d]: %v", pr.ID, err)
 		}
 	}

services/pull/pull.go

@@ -120,7 +120,7 @@ func ChangeTargetBranch(pr *models.PullRequest, doer *models.User, targetBranch
 	if pr.Status == models.PullRequestStatusChecking {
 		pr.Status = models.PullRequestStatusMergeable
 	}
-	if err := pr.UpdateCols("status, conflicted_files, base_branch"); err != nil {
+	if err := pr.UpdateColsIfNotMerged("merge_base", "status", "conflicted_files", "base_branch"); err != nil {
 		return err
 	}