[LyX/master] Compile fix for mingw

[Enrico Forestieri]

commit d5567ac36f65b31aaf4e1c055c966f15e2bbc94b
Author: Enrico Forestieri <for...@lyx.org>
Date:   Sat Apr 27 12:53:05 2019 +0200

    Compile fix for mingw
    
    This was probably overlooked at [7bb08f10/lyxgit].
---
 src/support/userinfo.cpp |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/support/userinfo.cpp b/src/support/userinfo.cpp
index 30a7c54..4496a28 100644
--- a/src/support/userinfo.cpp
+++ b/src/support/userinfo.cpp
@@ -42,7 +42,7 @@ string const user_name()
        char name[UNLEN + 1];
        DWORD size = UNLEN + 1;
        if (!GetUserName(name, &size))
-               return _("Unknown user");
+               return to_utf8(_("Unknown user"));
        return to_utf8(from_local8bit(name));
 #else
        struct passwd * pw = getpwuid(geteuid());