JS backend: fixed bug with the sourcemap generation when binary operation used as statement.

js/js.translator/testFiles/sourcemap/cases/binaryOperation.kt

@@ -0,0 +1,10 @@
+package foo
+
+fun box(): String {
+    1 * 2 / 3
+
+    var ok = ""
+    ok += "O" + "K"
+
+    return ok
+}