JS: inline safe calls

#KT-6912 fixed

js/js.translator/testData/inline/cases/safeCall.kt

@@ -0,0 +1,15 @@
+package foo
+
+// CHECK_CONTAINS_NO_CALLS: sum
+
+inline fun <T : Any, R> T.doLet(f: (T) -> R): R = f(this)
+
+private fun sum(x: Int?, y: Int): Int =
+        x?.doLet { it + y } ?: 0
+
+fun box(): String {
+    assertEquals(5, sum(2, 3))
+    assertEquals(0, sum(null, 3))
+
+    return "OK"
+}