Still some style problems with 8.3 branch

[Philippe Waroquiers <philippe dot waroquiers at skynet dot be>]

I just encountered a styling problem with the 8.3 branch
(also on the 8.4).
Test executed with GNU gdb (GDB) 8.2.91.20190330-git

To reproduce:
  ./gdb/gdb ./gdb/gdb
  info sources
and then type return successively, to see each page.
After the initial page, the first line contains a file that
is partially printed in green color, partially printed in black color,
e.g., in the below given output.
The line that starts with '--Type <RET>' is in black, as expected.
Then the next line starts in green as expected.
But only '/bd/home/ph' is in green.
We then have 'ilippe/gdb/git/relbranch/gdb/minsyms.h,' in black.
Then all is normal till the next page.

So, that seems to point at some remaining problem in the
buffering/output of style/color codes.

Philippe


...
/usr/include/regex.h, /bd/home/philippe/gdb/git/relbranch/gdb/gdb_regex.h, /bd/home/philippe/gdb/git/relbranch/gdb/command.h, 
/bd/home/philippe/gdb/git/relbranch/gdb/cli/cli-decode.h, /bd/home/philippe/gdb/git/relbranch/gdb/completer.h, /bd/home/philippe/gdb/git/relbranch/gdb/block.h, 
--Type <RET> for more, q to quit, c to continue without paging--
/bd/home/philippe/gdb/git/relbranch/gdb/minsyms.h, /bd/home/philippe/gdb/git/relbranch/gdb/ax.h, /bd/home/philippe/gdb/git/relbranch/gdb/probe.h, 
/bd/home/philippe/gdb/git/relbranch/gdb/language.h, /bd/home/philippe/gdb/git/relbranch/gdb/expression.h, /bd/home/philippe/gdb/git/relbranch/gdb/frame.h, 
...