Make 'namePos' return 'NoPosition' if name is 'nme.ERROR'

'namePos' used to return nonsensical position when the tree was
malformed (e.g. "case class").

Author: allanrenucci

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -337,10 +337,10 @@ object Trees {
      *  a calling chain from `viewExists`), in that case the return position is NoPosition.
      */
     def namePos =
-      if (pos.exists)
+      if (pos.exists && name.toTermName != nme.ERROR)
         if (rawMods.is(Synthetic)) Position(pos.point, pos.point)
         else Position(pos.point, pos.point + name.stripModuleClassSuffix.lastPart.length, pos.point)
-      else pos
+      else NoPosition
   }
 
   /** A ValDef or DefDef tree */