JS: Add test showing missing flow

javascript/ql/test/library-tests/TaintTracking/summarize-store-load-in-call.js

@@ -0,0 +1,12 @@
+import * as dummy from 'dummy';
+
+function blah(obj) {
+    obj.prop = obj.prop + "x";
+    return obj.prop;
+}
+
+function test() {
+    sink(blah(source())); // NOT OK
+
+    blah(); // ensure more than one call site exists
+}