[LyX/master] Do not duplicate jpg format

[Georg Baum]

commit 8d255ced2a003b2b8262bf51d1b245ff0dee9dc3
Author: Georg Baum <b...@lyx.org>
Date:   Thu Jun 2 22:31:27 2016 +0200

    Do not duplicate jpg format
    
    Some qt versions report both "jpeg" and "jpg" as loadable file extensions.
    In this case the jpg format was added twice previously. This does not happen
    anymore with the new code, and it works as well if only "jpg" or only "jpeg"
    is reported.

diff --git a/src/frontends/qt4/GuiApplication.cpp 
b/src/frontends/qt4/GuiApplication.cpp
index b3efd78..1513636 100644
--- a/src/frontends/qt4/GuiApplication.cpp
+++ b/src/frontends/qt4/GuiApplication.cpp
@@ -227,14 +227,25 @@ vector<string> loadableImageFormats()
        if (qt_formats.empty())
                LYXERR(Debug::GRAPHICS, "\nQt4 Problem: No Format available!");
 
+       bool jpeg_found = false;
+       bool jpg_found = false;
        for (QList<QByteArray>::const_iterator it = qt_formats.begin(); it != 
qt_formats.end(); ++it) {
 
                LYXERR(Debug::GRAPHICS, (const char *) *it << ", ");
 
                string ext = ascii_lowercase((const char *) *it);
                // special case
-               if (ext == "jpeg")
+               if (ext == "jpeg") {
+                       jpeg_found = true;
+                       if (jpg_found)
+                               continue;
                        ext = "jpg";
+               }
+               else if (ext == "jpg") {
+                       jpg_found = true;
+                       if (jpeg_found)
+                               continue;
+               }
                fmts.push_back(ext);
        }