Add failsafe for a case where prefixes in CheckUnused/prepareIndent formed an infinite cycle

Author: szymon-rd

compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -78,6 +78,7 @@ class CheckUnused extends MiniPhase:
   override def prepareForIdent(tree: tpd.Ident)(using Context): Context =
     if tree.symbol.exists then
       val prefixes = LazyList.iterate(tree.typeOpt.normalizedPrefix)(_.normalizedPrefix).takeWhile(_ != NoType)
+        .take(10) // Failsafe in the odd case if there were an infinite cycle
       for {
         prefix <- prefixes
       } {