Initialise the internal buffer before handing it to the reader

[icedracon]

Fixes #9.

with_capacity called set_len on a Vec that was never written to, and fill_buf passes that buffer straight to the wrapped Read impl. Read::read only recommends against reading buf rather than forbidding it, so an implementation that inspects its buffer observed uninitialised memory.

Miri on the current release:

error: Undefined Behavior: reading memory at alloc46971[0x0..0x1],
       but memory is uninitialized at [0x0..0x1],
       and this operation requires initialized memory
   = note: stack backtrace:
      0: <PeekingReader as std::io::Read>::read
      3: <RevBufReader<PeekingReader> as std::io::BufRead>::fill_buf
           at src/lib.rs:401:13

Change

Allocate a zeroed buffer instead:

let buffer = vec![0; capacity];

std::io::BufReader shipped exactly this for years before moving to BorrowedBuf/read_buf.

This also drops the inner.initializer().initialize(&mut buffer) call. That path sat behind feature = "read_initializer", which needs the #![feature(read_initializer)] nightly gate — a language feature that has since been removed from the compiler, so it could not be enabled on any current toolchain. The read_initializer feature flag itself and the Read::initializer impl are left alone; removing them is a separate cleanup if you want it.

Verification

• new regression test test_buffer_handed_to_reader_is_initialized
• existing suite passes (11 unit + 10 integration)
• cargo +nightly miri test clean on the patched crate

Happy to adjust anything.