Revert suspicious widening of getter's result type

Author: adriaanm

src/compiler/scala/tools/nsc/typechecker/MethodSynthesis.scala

@@ -395,12 +395,13 @@ trait MethodSynthesis {
         // starts compiling (instead of failing like it's supposed to) because the typer
         // expects to be able to identify escaping locals in typedDefDef, and fails to
         // spot that brand of them. In other words it's an artifact of the implementation.
-        val tpt = derivedSym.tpe_*.finalResultType.widen match {
+        val getterTp = derivedSym.tpe_*.finalResultType
+        val tpt = getterTp.widen match {
           // Range position errors ensue if we don't duplicate this in some
           // circumstances (at least: concrete vals with existential types.)
-          case ExistentialType(_, _)  => TypeTree() setOriginal (tree.tpt.duplicate setPos tree.tpt.pos.focus)
-          case _ if isDeferred        => TypeTree() setOriginal tree.tpt // keep type tree of original abstract field
-          case tp                     => TypeTree(tp)
+          case _: ExistentialType => TypeTree() setOriginal (tree.tpt.duplicate setPos tree.tpt.pos.focus)
+          case _ if isDeferred    => TypeTree() setOriginal tree.tpt // keep type tree of original abstract field
+          case _                  => TypeTree(getterTp)
         }
         tpt setPos tree.tpt.pos.focus
       }