C++: Add some test cases from cpp/empty-if to the test for cpp/empty-block (exploring overlap).

Author: geoffw0

cpp/ql/test/query-tests/Best Practices/Likely Errors/EmptyBlock/EmptyBlock.expected

@@ -1,3 +1,7 @@
 | empty_block.cpp:9:10:9:11 | { ... } | Empty block without comment. |
 | empty_block.cpp:12:10:13:3 | { ... } | Empty block without comment. |
 | empty_block.cpp:20:10:21:3 | { ... } | Empty block without comment. |
+| empty_block.cpp:84:14:85:3 | { ... } | Empty block without comment. |
+| empty_block.cpp:93:10:94:3 | { ... } | Empty block without comment. |
+| empty_block.cpp:99:10:100:3 | { ... } | Empty block without comment. |
+| empty_block.cpp:100:10:101:3 | { ... } | Empty block without comment. |

cpp/ql/test/query-tests/Best Practices/Likely Errors/EmptyBlock/empty_block.cpp

@@ -80,5 +80,25 @@ int f(int x) {
     }
   }
 
+  // BAD
+  if (x > 1) {
+  }
+
+  // GOOD
+  if (x) {
+    ++x;
+  }
+
+  // DUBIOUS (reported)
+  if (x) {
+  } else {
+    ++x;
+  }
+
+  // BAD (x2)
+  if (x) {
+  } else {
+  }
+
   return 1;
 }