checkpatch: don't print the next line if not defined

checkpatch: don't print the next line if not defined

When checking if "Reported-by" tag is followed by "Link:", there is no
need to print the next line if there is no next line.

While at it, also mention in this case that the "Link:" tag should be
followed by a URL, similar to the next warning.

By doing that, the code is now similar to what is done above when checking
if the Co-developed-by tag is properly used.

Link: https://lkml.kernel.org/r/20230314-doc-checkpatch-closes-tag-v4-2-d26d1fa66f9f@tessares.net
Fixes: d7f1d71e5ef6 ("checkpatch: warn when Reported-by: is not followed by Link:")
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Acked-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@gmail.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kai Wasserbäch <kai@dev.carbon-project.org>
Cc: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>