fixed 2 warnings with -Wsign-compare

Interestingly, changing the line to something like
```c++
BOOST_STATIC_ASSERT(dataAlignment > 0U);
```
```c++
BOOST_STATIC_ASSERT(dataAlignment > (uint32)0);
```
```c++
BOOST_STATIC_ASSERT(dataAlignment > static_cast<unsigned>(0));
```
did **not** work :confused: