C++: Consider writes to arrays as uncertain

[MathiasVP]

This PR fixes a bug where we were incorrectly concluding that a write such as:

int xs[10];
*xs = 42;

would overwrite the entire object.

Commit-by-commit review recommended (even though the fix is extremely straightforward).

[MathiasVP]

Two new DCA results:

• The cpp/path-injection one looks genuine
• The cpp/potential-system-data-exposure is a FP because Samate doesn't consider usernames sensitive, but this query does.