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.translator/testData/expression/when/cases/ifInWhenDanglingElseIssue.kt

@@ -0,0 +1,27 @@
+// http://youtrack.jetbrains.com/issue/KT-5253
+// JS: generated wrong code when use `if` inside `when`
+
+package foo
+
+
+fun test(caseId: Int, value: Int, expected: Int) {
+    var actual: Int = 0
+    when (caseId) {
+        2 -> if (value < 0) actual = -value
+        3 -> actual = if (value < 0) {-value} else value
+        else -> throw Exception("Unexpected case: $caseId")
+    }
+
+    if (expected != actual) throw Exception("expected = $expected, actual = $actual")
+}
+
+
+fun box(): String {
+
+    test(2, 33, 0)
+    test(2, -1, 1)
+    test(3, 23, 23)
+    test(3, -3, 3)
+
+    return "OK"
+}