Another compensation for c64e676

TermRefs that do not have a symbol should not be widened under widenIfUnstable.

Author: odersky

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1082,7 +1082,7 @@ object Types {
     /** Widen type if it is unstable (i.e. an ExprType, or TermRef to unstable symbol */
     final def widenIfUnstable(implicit ctx: Context): Type = stripTypeVar match {
       case tp: ExprType => tp.resultType.widenIfUnstable
-      case tp: TermRef if !tp.symbol.isStableMember => tp.underlying.widenIfUnstable
+      case tp: TermRef if tp.symbol.exists && !tp.symbol.isStableMember => tp.underlying.widenIfUnstable
       case _ => this
     }