add test for new barrier

Author: erik-krogh

javascript/ql/test/library-tests/TaintTracking/BasicTaintTracking.expected

@@ -79,6 +79,8 @@ typeInferenceMismatch
 | sanitizer-guards.js:43:11:43:18 | source() | sanitizer-guards.js:45:8:45:8 | x |
 | sanitizer-guards.js:43:11:43:18 | source() | sanitizer-guards.js:48:10:48:10 | x |
 | sanitizer-guards.js:68:11:68:18 | source() | sanitizer-guards.js:75:8:75:8 | x |
+| sanitizer-guards.js:79:11:79:18 | source() | sanitizer-guards.js:81:8:81:8 | x |
+| sanitizer-guards.js:79:11:79:18 | source() | sanitizer-guards.js:84:10:84:10 | x |
 | spread.js:2:15:2:22 | source() | spread.js:4:8:4:19 | { ...taint } |
 | spread.js:2:15:2:22 | source() | spread.js:5:8:5:43 | { f: 'h ... orld' } |
 | spread.js:2:15:2:22 | source() | spread.js:7:8:7:19 | [ ...taint ] |

javascript/ql/test/library-tests/TaintTracking/sanitizer-guards.js

@@ -74,3 +74,15 @@ function phi2() {
   }
   sink(x); // NOT OK
 }
+
+function falsy() {
+  let x = source();
+  
+  sink(x); // NOT OK
+  
+  if (x) {
+    sink(x); // NOT OK
+  } else {
+	sink(x); // OK
+  }
+}