appDisplay: Handle non-UTF8 filename encodings more gracefully

It may be 2015, but users still stumble upon the occasional .desktop
file that uses a filename encoding other than UTF-8. We currently
fail quite spectacularly in that case by not displaying any apps at
all - handle this case more gracefully, by only filtering out the
offending apps.

https://bugzilla.gnome.org/show_bug.cgi?id=651503

src/shell-app-system.h

@@ -48,5 +48,6 @@ ShellApp       *shell_app_system_lookup_desktop_wmclass       (ShellAppSystem *s
                                                                const char     *wmclass);
 
 GSList         *shell_app_system_get_running               (ShellAppSystem  *self);
+char         ***shell_app_system_search                    (const char *search_string);
 
 #endif /* __SHELL_APP_SYSTEM_H__ */