Add base repo nil check (#5555)

Signed-off-by: Jonas Franz <info@jonasfranz.software>

models/pull.go

@@ -113,6 +113,15 @@ func (pr *PullRequest) loadIssue(e Engine) (err error) {
 
 // LoadProtectedBranch loads the protected branch of the base branch
 func (pr *PullRequest) LoadProtectedBranch() (err error) {
+	if pr.BaseRepo == nil {
+		if pr.BaseRepoID == 0 {
+			return nil
+		}
+		pr.BaseRepo, err = GetRepositoryByID(pr.BaseRepoID)
+		if err != nil {
+			return
+		}
+	}
 	pr.ProtectedBranch, err = GetProtectedBranchBy(pr.BaseRepo.ID, pr.BaseBranch)
 	return
 }