justification after @center

[Akim Demaille]

There seems to be a good dynamic at killing bugs currently :)
I can't resist resubmitting one that affects a document of mine.

Thanks!

~/src/texinfo % eof test-cases/post-center-wrapping.texi         nostromo 13:01
: -------------------- test-cases/post-center-wrapping.texi 
----------------------
cat > test-cases/post-center-wrapping.texi << \EOF
\input texinfo   @c -*-texinfo-*-
@setfilename error
@settitle error

@ifnottex
@node Top
@top TITLE
@end ifnottex

@center This is centered.

This is so incorrectly justified! This is so incorrectly justified!
This is so incorrectly justified! This is so incorrectly justified!
This is so incorrectly justified! This is so incorrectly justified!
This is so incorrectly justified! This is so incorrectly justified!
This is so incorrectly justified!

@bye
EOF
: ------------------------------------------------------------
~/src/texinfo % makeinfo --no-header < test-cases/post-center-wrapping.texi
TITLE
*****

                           This is centered.
 This is so incorrectly justified! This is so
incorrectly justified!  This is so incorrectly justified! This is so
incorrectly justified!  This is so incorrectly justified! This is so
incorrectly justified!  This is so incorrectly justified! This is so
incorrectly justified!  This is so incorrectly justified!