C++: Add query precision.

Author: geoffw0

cpp/ql/src/experimental/Security/CWE/CWE-190/AllocMultiplicationOverflow.ql

@@ -3,7 +3,7 @@
  * @description Using a multiplication result that may overflow in the size of an allocation may lead to buffer overflows when the allocated memory is used.
  * @kind path-problem
  * @problem.severity warning
- * @precision TODO
+ * @precision low
  * @tags security
  *       correctness
  *       external/cwe/cwe-190