C++: Add FP test.

Author: MathiasVP

cpp/ql/test/query-tests/Critical/MissingCheckScanf/IncorrectCheckScanf.expected

@@ -3,3 +3,4 @@
 | test.cpp:204:7:204:11 | call to scanf | The result of scanf is only checked against 0, but it can also return EOF. |
 | test.cpp:436:7:436:11 | call to scanf | The result of scanf is only checked against 0, but it can also return EOF. |
 | test.cpp:443:11:443:15 | call to scanf | The result of scanf is only checked against 0, but it can also return EOF. |
+| test.cpp:467:8:467:12 | call to scanf | The result of scanf is only checked against 0, but it can also return EOF. |

cpp/ql/test/query-tests/Critical/MissingCheckScanf/test.cpp

@@ -458,4 +458,18 @@ void disjunct_boolean_condition(const char* modifier_data) {
 		return;
 	}
 	use(value); // GOOD
+}
+
+void check_for_negative_test() {
+	int res;
+	int value;
+
+	res = scanf("%d", &value); // GOOD [FALSE POSITIVE]
+	if(res == 0) {
+		return;
+	}
+	if (res < 0) {
+		return;
+	}
+	use(value);
 }