od: print valid octal values with -c flag

For characters with the top bit set od_bloaty produces silly octal
values with the -c flag:

$ echo £ | busybox od -c   # od_bloaty.c (CONFIG_DESKTOP set)
0000000 0H2 0D3  \n
0000003
$ echo £ | busybox od -c   # od.c (CONFIG_DESKTOP not set)
0000000  302 243  \n
0000003
$ echo £ | od -c           # coreutils
0000000 302 243  \n
0000003
vi: failure to open file is not an error when initialising buffer

Commit 32afd3a introduced these regressions on the master branch:

Starting vi with no filename on the command line gives the status message
"'(null)' Bad address" instead of "- No file 1/1 100%".

Starting vi with a non-existent file on the command line gives the status
message "'new.txt' No such file or directory" instead of "- new.txt 1/1 100%"
vi: fix reading of file after last line

If the :r command is used to read a file after the last line of the
buffer the last line of the buffer and the first line of the file
are joined.  An extra blank line appears at the end of the buffer.

   file 1
   file 1
   file 1file 2
   file 2
   file 2

	~
	~

The insertion point is normally at the start of the line following the
specified line.  When the specified line is the last one the next_line
function baulks at moving to the non-existent following line.