fix runtime asan error due to storing to and reading from misaligned address

[TylkoKuba]

local blob = lovr.data.newBlob(3)
blob:setU8(0, 0)
blob:setU16(1, 0)
blob:getU8(0)
blob:getU16(1)

Results in
runtime error: store to misaligned address [...] for type 'uint16_t' (aka 'unsigned short'), which requires 2 byte alignment
and
runtime error: load of misaligned address [...] for type 'const uint16_t' (aka 'const unsigned short'), which requires 2 byte alignment

[bjornbytes]

Thanks!