fix several compiler warnings

Author: ammen99

src/panel/widgets/menu.cpp

@@ -230,8 +230,6 @@ bool WayfireMenu::update_icon()
 {
     std::string icon;
     int size = menu_size / LAUNCHERS_ICON_SCALE;
-    bool error = false;
-
     if (((std::string) menu_icon).empty())
     {
         icon = default_icon;

src/util/gtk-utils.cpp

@@ -10,13 +10,13 @@ Glib::RefPtr<Gdk::Pixbuf> load_icon_pixbuf_safe(std::string icon_path, int size)
     {
         auto pb = Gdk::Pixbuf::create_from_file(icon_path, size, size);
         return pb;
-    } 
-    catch(Glib::FileError)
+    }
+    catch(Glib::FileError&)
     {
         std::cerr << "Error loading file: " << icon_path << std::endl;
         return {};
     }
-    catch(Gdk::PixbufError)
+    catch(Gdk::PixbufError&)
     {
         std::cerr << "Pixbuf error: " << icon_path << std::endl;
         return {};