ANDROID: ring-buffer: Handle external writer reader_page fast-forward

In order to support dump on panic, the external writer might
fast-forward the reader-page to make sure the very last events can be
read.

Bug: 357781595
Bug: 391974813
Change-Id: I5b2473756a3350de8b0b808b54df662b8a77c6ad
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>