CQ shared: Fix off-by-nine error leading to lost messages

And `eof` crashes.

The problem is that we may end up trying to read more data
from the file when scanning, despite being at the end of the
file. This results in the current Acc to be returned instead
of the remaining data being parsed.

This results in some messages at the end of the file being
truncated off despite still being in memory (and still pointing
to the end of the original file, well past the truncation point).

Author: lhoguin

deps/rabbit/src/rabbit_msg_store.erl

@@ -1599,7 +1599,7 @@ scan_data(<<Size:64, MsgIdInt:128, _Rest/bits>> = Data, Fd, Fun, Offset, FileSiz
     end;
 %% This might be the start of a message.
 scan_data(<<Size:64, Rest/bits>> = Data, Fd, Fun, Offset, FileSize, MsgIdsFound, Acc)
-          when byte_size(Rest) < Size + 1, Size < FileSize - Offset ->
+          when byte_size(Rest) < Size + 1, Size + 8 < FileSize - Offset ->
     scan(Data, Fd, Fun, Offset, FileSize, MsgIdsFound, Acc);
 scan_data(Data, Fd, Fun, Offset, FileSize, MsgIdsFound, Acc)
           when byte_size(Data) < 8 ->