packets: replace repeated if/else if by switch (#580)

packets.go

@@ -486,23 +486,24 @@ func (mc *mysqlConn) readResultOK() ([]byte, error) {
 				plugin := string(data[1:pluginEndIndex])
 				cipher := data[pluginEndIndex+1 : len(data)-1]
 
-				if plugin == "mysql_old_password" {
+				switch plugin {
+				case "mysql_old_password":
 					// using old_passwords
 					return cipher, ErrOldPassword
-				} else if plugin == "mysql_clear_password" {
+				case "mysql_clear_password":
 					// using clear text password
 					return cipher, ErrCleartextPassword
-				} else if plugin == "mysql_native_password" {
+				case "mysql_native_password":
 					// using mysql default authentication method
 					return cipher, ErrNativePassword
-				} else {
+				default:
 					return cipher, ErrUnknownPlugin
 				}
-			} else {
-				// https://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::OldAuthSwitchRequest
-				return nil, ErrOldPassword
 			}
 
+			// https://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::OldAuthSwitchRequest
+			return nil, ErrOldPassword
+
 		default: // Error otherwise
 			return nil, mc.handleErrorPacket(data)
 		}