Fix some trivial problems (#36336)

1. correctly parse git protocol's "OldCommit NewCommit RefName" line, it
should be explicitly split by space
2. add missing "return" in CreatePullRequest
3. add comments for "/user.keys" and "/user.gpg" outputs
4. trim space for the "commit status context name" to follow the same
behavior of git_model.NewCommitStatus

routers/api/v1/repo/pull.go

@@ -500,6 +500,7 @@ func CreatePullRequest(ctx *context.APIContext) {
 	unitPullRequest, err := ctx.Repo.Repository.GetUnit(ctx, unit.TypePullRequests)
 	if err != nil {
 		ctx.APIErrorInternal(err)
+		return
 	}
 
 	prIssue := &issues_model.Issue{