Fix isWildcard

Code inspection revealed that it did the wrong thing for annotated trees,
looking in the annotation instead of in the argument.

Author: odersky

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

@@ -339,7 +339,7 @@ object Parsers {
     def isWildcard(t: Tree): Boolean = t match {
       case Ident(name1) => placeholderParams.nonEmpty && name1 == placeholderParams.head.name
       case Typed(t1, _) => isWildcard(t1)
-      case Annotated(t1, _) => isWildcard(t1)
+      case t: Annotated => isWildcard(t.arg)
       case Parens(t1) => isWildcard(t1)
       case _ => false
     }