JS: fix crash when js function contains for statement w/o initializer

Fix KT-20898

js/js.translator/testData/box/jsCode/forWithoutInit.kt

@@ -0,0 +1,20 @@
+// EXPECTED_REACHABLE_NODES: 1125
+// FILE: a.kt
+fun foo(n: Int): String = js("""
+    var result = "";
+
+    var i = 0;
+    for (; i < n; i++) {
+        result += i + ";"
+    }
+
+    return result;
+""")
+
+// FILE: b.kt
+// RECOMPILE
+fun box(): String {
+    val r = foo(3)
+    if (r != "0;1;2;") return "fail: $r"
+    return "OK"
+}