[LyX/master] Fix warning about signed/unsigned

[Jean-Marc Lasgouttes]

commit a98df5853719256139977e5de0146f3604af9975
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Wed Jun 7 11:05:29 2017 +0200

    Fix warning about signed/unsigned
---
 src/insets/InsetListings.cpp |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/insets/InsetListings.cpp b/src/insets/InsetListings.cpp
index 0693b5a..b5a5701 100644
--- a/src/insets/InsetListings.cpp
+++ b/src/insets/InsetListings.cpp
@@ -125,7 +125,7 @@ void InsetListings::latex(otexstream & os, OutputParams 
const & runparams) const
                // then remove the relative options.
                vector<string> opts =
                        getVectorFromString(param_string, ",", false);
-               for (int i = 0; i < opts.size(); ++i) {
+               for (size_t i = 0; i < opts.size(); ++i) {
                        if (prefixIs(opts[i], "float")) {
                                if (prefixIs(opts[i], "float="))
                                        float_placement = opts[i].substr(6);