[LyX/2.2.x] Fix filter filter regex

[Georg Baum]

commit 1cbc3b6e549cc68424d707cd5d8fe1a856a25899
Author: Georg Baum <b...@lyx.org>
Date:   Thu Sep 8 20:54:13 2016 +0200

    Fix filter filter regex
    
    Now the external material file dialog shows the file types defined in the
    template again. Before this fix it did only show "All files (*)".
    I don't know what the old syntax was supposed to do or whether it ever 
worked
    with boost::regex, but with std::regex the new one is correct.
---
 src/frontends/qt4/qt_helpers.cpp |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/frontends/qt4/qt_helpers.cpp b/src/frontends/qt4/qt_helpers.cpp
index c1294e5..655cbea 100644
--- a/src/frontends/qt4/qt_helpers.cpp
+++ b/src/frontends/qt4/qt_helpers.cpp
@@ -556,7 +556,7 @@ FileFilterList::FileFilterList(docstring const & 
qt_style_filter)
 
                // Everything from the start of the input to
                // the start of the match.
-               parse_filter(string(what[-1].first, what[-1].second));
+               parse_filter(string(it, what[0].first));
 
                // Increment the iterator to the end of the match.
                it += distance(it, what[0].second);