JS backend: fix dangling else issue in generated code for JsToStringGenerationVisitor

JS backend: fix KT-5253: when with if inside

 #KT-5253 Fixed

js/js.tests/test/org/jetbrains/k2js/test/semantics/WhenTest.java

@@ -108,4 +108,8 @@ public final class WhenTest extends AbstractExpressionTest {
     public void testWhenWithOneStmWhen() throws Exception {
         fooBoxTest();
     }
+
+    public void testIfInWhenDanglingElseIssue() throws Exception {
+        checkFooBoxIsOk();
+    }
 }