Remove g_lambda_cost
Moved g_cur_lambda_cost into encoder_control.cur_lambda_cost
Address a clang-analyzer warning about undefined behavior in filter.

- Analyzer didn't see that code is never called with MAX_DEPTH as it doesn't
  know the properties of width, height, x and y. Following would also
  silence the error:
    assert(cur_pic->width > 0 && cur_pic->height > 0);
    assert(cur_pic->width % 8 == 8 && cur_pic->height % 8 == 0);
    assert(x > 0 && y > 0);
    assert(x % 8 == 0 && y % 8 == 0);

- Related to issue #35.
Address clang-analyzer warning about undefined behavior in intra.

- Related to issue #35.
Address clang-analyzer warnings about unused values.

- Related to issue #35.
Address clang-analyzer warnings about garbage values.

- False alarm, but surprisingly difficult to convince clang of that. It
  doesn't seem to understand bit shifts very well.

- Only assert and changing LCU_WIDTH>>depth to width was necessary to satisfy
  clang.

- Closes #35.