Visit Stmt children for null deref check.
Visit Stmt children for null deref check.

The previous version of the Null deref visitor was defaulting to
VisitStmt when the Stmt type was unknown, thus allowing for some
types of Stmt X for which a VisitX was not implemented to default
to VisitStmt and not check the content of it. In order to check
any type of Stmt for possible subexpressions which contain s Stmt
that derefrences a Null, the VisitStmt was extended to check its
children.

Only the Stmt types, X, which directly containing a null deref expression
have an explicit VisitX with the exception of CXXMemberCallExpr,
because this type would otherwise default to VisitCallExpr which has
a different check for its structure.

marsupial/cling,root-mirror/cling,root-mirror/cling,karies/cling,marsupial/cling,karies/cling,marsupial/cling,root-mirror/cling,marsupial/cling,karies/cling,marsupial/cling,root-mirror/cling,root-mirror/cling,karies/cling,root-mirror/cling,karies/cling,marsupial/cling,karies/cling