Added more error handling to the nativefont. Also changed the

code so that the native font object isn't instantiated unless
you try to use it for something.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402454

dlib/gui_core/gui_core_kernel_2.cpp

@@ -24,7 +24,6 @@
 #include "../logger.h"
 #include <vector>
 #include <set>
-#include "../gui_widgets/fonts.h"
 
 namespace dlib
 {
@@ -1570,7 +1569,8 @@ namespace dlib
             int mcount;
             char *def_str;
             char fontset[256];
-            sprintf(fontset, "-*-*-medium-r-normal--%lu-*-*-*-", get_native_font()->height());
+            const long native_font_height = 12;
+            sprintf(fontset, "-*-*-medium-r-normal--%lu-*-*-*-", native_font_height);
             XFontSet fs = XCreateFontSet(gui_core_kernel_2_globals::disp, fontset, &mlist, &mcount, &def_str);
             xpoint.x = 0;
             xpoint.y = 0;

dlib/gui_widgets/nativefont.h

@@ -372,6 +372,8 @@ namespace nativefont
                             XFreeFontSet(d, fs);
                         }
                         fs = XCreateFontSet(d, fontset, &mlist, &mcount, &def_str);
+                        if (fs == NULL)
+                           throw dlib::gui_error("gui_error: XCreateFontSet() failure");
 
                         XFontSetExtents *extent;
                         extent = XExtentsOfFontSet(fs);