[CPP-434] Additional test case; improve QHelp by including themes from the BadAdditionOverflowCheck QHelp.

cpp/ql/test/query-tests/Likely Bugs/Arithmetic/BadAdditionOverflowCheck/SignedOverflowCheck.cpp

@@ -112,3 +112,7 @@ bool multipleCasts2(char x) {
     // msvc 19.22 /O2: not deleted
     return (int)(unsigned short)(x + '1') < (int)(unsigned short)x; // GOOD [FALSE POSITIVE]
 }
+
+int does_it_overflow(int n1, unsigned short delta) {
+    return n1 + (unsigned)delta < n1; // GOOD
+}