Open transaction when adding Avatar email-hash pairs to the DB (#12577) (#12940)

Backport #12577

When adding Avatar email-hash pairs we simply want the DB table to
represent a Set. We don't care if the hash-pair is already present,
so we just simply Insert and ignore the error.

Unfortunately this seems to cause some DBs to log the duplicate
insert to their logs - looking like a bug a in Gitea.

Now, there is no standard way in SQL to say Insert but if there's
an error ignore it. MySQL has INSERT IGNORE, PostgreSQL >= 9.5 has
INSERT ... ON CONFLICT DO NOTHING, but I do not believe that SQLite
or MSSQL have variants.

This PR places the insert in a transaction which we are happy to fail
if there is an error - hopefully this will stop the unnecessary
logging.

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

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

models/avatar.go

@@ -41,7 +41,18 @@ func AvatarLink(email string) string {
 			Email: lowerEmail,
 			Hash:  sum,
 		}
-		_, _ = x.Insert(emailHash)
+		// OK we're going to open a session just because I think that that might hide away any problems with postgres reporting errors
+		sess := x.NewSession()
+		defer sess.Close()
+		if err := sess.Begin(); err != nil {
+			// we don't care about any DB problem just return the lowerEmail
+			return lowerEmail, nil
+		}
+		_, _ = sess.Insert(emailHash)
+		if err := sess.Commit(); err != nil {
+			// Seriously we don't care about any DB problems just return the lowerEmail - we expect the transaction to fail most of the time
+			return lowerEmail, nil
+		}
 		return lowerEmail, nil
 	})
 	return setting.AppSubURL + "/avatar/" + url.PathEscape(sum)