Fix minimum bufsize problem

[bhollemb]

If the upper bound of the buffer size is less than sizeof(dword), memory corruption will occur and cause crashes in DIBF. It appears to be related to the following line, but this assumption may occur elsewhere as well.

"if(position<ioStore[ioctlIndex].dwUpperSize-sizeof(DWORD)) {" https://github.com/iSECPartners/DIBF/blob/master/dibf/FuzzingProvider.cpp#L91