Parsers.scala: support multiple if-guards on same line

Author: unkarjedy

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2483,7 +2483,7 @@ object Parsers {
       else Nil
 
     /** Enumerator  ::=  Generator
-     *                |  Guard
+     *                |  Guard {Guard}
      *                |  Pattern1 `=' Expr
      */
     def enumerator(): Tree =