[LyX/master] Fix warning with --disable-nls

[Jean-Marc Lasgouttes]

commit 4f4d52e8c09d798359071590ed3624ecaa5b2b8a
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Mon Jan 27 15:34:27 2020 +0100

    Fix warning with --disable-nls
---
 src/support/Messages.cpp |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/support/Messages.cpp b/src/support/Messages.cpp
index 94d34ca..842697e 100644
--- a/src/support/Messages.cpp
+++ b/src/support/Messages.cpp
@@ -386,7 +386,7 @@ bool Messages::available(string const & /* c */)
 	return false;
 }
 
-docstring const Messages::getIfFound(string const & m) const
+docstring const Messages::getIfFound(string const & /* m */) const
 {
 	return docstring();
 }