View-pure checker misses reads from storage pointer variable

```
contract Storage {
struct S { uint x; }
S t;

function store(S storage x) internal {
S memory y = x;
}

function f() public {
store(t);
}
}
```
Function `store` is considered `pure`. Same if `x` is used in function call conversion to memory. Reading members from `x` is properly detected.