FUSE: Process crashes when creating file

[rs22]

This issue was introduced when we started writing data in 4KB bursts.

Apparently, there's not enough memory allocated on the host side (i.e. not a multiple of 4KB), so the memory operator overwrites heap metadata, which leads to an exception when calling free() on the buffer later on. We have to make sure that our input/output buffers are always 4KB-aligned and multiples of 4KB in size.