Fix a few more MSVC level 3 warnings

 cbor.h(278): warning C4800: 'const uint16_t': forcing value to bool 'true' or 'false' (performance warning)
 cborencoder.c(295): warning C4334: '<<': result of 32-bit shift implicitly converted to 64 bits (was 64-bit shift
 cborparser.c(677): warning C4800: 'uintptr_t': forcing value to bool 'true' or 'false' (performance warning)

Signed-off-by: Thiago Macieira <thiago.macieira@intel.com>