C#: Add a testcase with an empty if statement containing a comment.

Author: michaelnebel

csharp/ql/test/query-tests/Useless Code/FutileConditional/FutileConditional.cs

@@ -25,5 +25,10 @@ public void M(string s)
         else
         {
         } // $ Alert
+
+        if (s.Length > 4)
+        {
+            // GOOD: Because of the comment.
+        }
     }
 }

csharp/ql/test/query-tests/Useless Code/FutileConditional/FutileConditional.expected

@@ -1,3 +1,7 @@
+#select
 | FutileConditional.cs:8:9:8:27 | if (...) ... | If-statement with an empty then-branch and no else-branch. |
 | FutileConditional.cs:10:9:12:9 | if (...) ... | If-statement with an empty then-branch and no else-branch. |
 | FutileConditional.cs:22:9:27:9 | if (...) ... | If-statement with an empty then-branch and no else-branch. |
+| FutileConditional.cs:29:9:32:9 | if (...) ... | If-statement with an empty then-branch and no else-branch. |
+testFailures
+| FutileConditional.cs:29:9:32:9 | If-statement with an empty then-branch and no else-branch. | Unexpected result: Alert |