Fix computation of 'entry_length' in AAPT2 container format

When the protobuf header (or data payload) size are a multiple of 4,
"entry_length" (called "aligned size" in the code) would have counted bytes that
are never actually written.

Bug: 139418052
Change-Id: Ia688a82a67f3807f7feb0be03670bf2827b1d6a1