Select the default scheme in the Color Scheme dialog by default

Always select the default scheme by default in the Color Scheme dialog
not to end up selecting none in case of broken or nonexistent
configuration.  This matches which scheme is actually used, and fixes
use of an uninitialized iter when no scheme would be selected.

src/highlighting.c

@@ -1249,7 +1249,10 @@ static void add_color_scheme_item(GtkListStore *store,
 		SCHEME_FILE, fn, -1);
 	g_free(markup);
 
-	if (utils_str_equal(fn, editor_prefs.color_scheme) && current_iter)
+	/* select the current iter if the the color scheme matches, or if it's the
+	 * default (fn == NULL), in case of bad config file.  the default theme is
+	 * first anyway so if a later scheme matches it will override default */
+	if ((! fn || utils_str_equal(fn, editor_prefs.color_scheme)) && current_iter)
 		*current_iter = iter;
 }