Prevent NPE whilst migrating if there is a team request review (#19855)

A pr.Reviewer may be nil when migrating from Gitea if this is a team
request review.

We do not migrate teams therefore we cannot map these requests, but we can
migrate user requests.

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

services/migrations/github.go

@@ -21,7 +21,7 @@ import (
 	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/util"
 
-	"github.com/google/go-github/v39/github"
+	"github.com/google/go-github/v45/github"
 	"golang.org/x/oauth2"
 )
 
@@ -778,6 +778,7 @@ func (g *GithubDownloaderV3) GetReviews(reviewable base.Reviewable) ([]*base.Rev
 	opt := &github.ListOptions{
 		PerPage: g.maxPerPage,
 	}
+	// Get approve/request change reviews
 	for {
 		g.waitAndPickClient()
 		reviews, resp, err := g.getClient().PullRequests.ListReviews(g.ctx, g.repoOwner, g.repoName, int(reviewable.GetForeignIndex()), opt)
@@ -817,5 +818,28 @@ func (g *GithubDownloaderV3) GetReviews(reviewable base.Reviewable) ([]*base.Rev
 		}
 		opt.Page = resp.NextPage
 	}
+	// Get requested reviews
+	for {
+		g.waitAndPickClient()
+		reviewers, resp, err := g.getClient().PullRequests.ListReviewers(g.ctx, g.repoOwner, g.repoName, int(reviewable.GetForeignIndex()), opt)
+		if err != nil {
+			return nil, fmt.Errorf("error while listing repos: %v", err)
+		}
+		g.setRate(&resp.Rate)
+		for _, user := range reviewers.Users {
+			r := &base.Review{
+				ReviewerID:   user.GetID(),
+				ReviewerName: user.GetLogin(),
+				State:        base.ReviewStateRequestReview,
+				IssueIndex:   reviewable.GetLocalIndex(),
+			}
+			allReviews = append(allReviews, r)
+		}
+		// TODO: Handle Team requests
+		if resp.NextPage == 0 {
+			break
+		}
+		opt.Page = resp.NextPage
+	}
 	return allReviews, nil
 }