Fix dynamic width check

The width_set field is true if the width is set in the geometry setting,
in other words if a specific (or dynamic) width is set or we want the
notification to cover the whole screen.
In order to check if a specific width is chosen we need to also exclude
dynamic width, meaning the width field has to be non 0;

Fixes #614

src/settings.c

@@ -432,7 +432,7 @@ void load_settings(char *cmdline_config_path)
         // restrict the icon size to a reasonable limit if we have a fixed width.
         // Otherwise the layout will be broken by too large icons.
         // See https://github.com/dunst-project/dunst/issues/540
-        if (settings.geometry.width_set) {
+        if (settings.geometry.width_set && settings.geometry.w != 0) {
                 const int icon_size_limit = settings.geometry.w / 2;
                 if (   settings.max_icon_size == 0
                     || settings.max_icon_size > icon_size_limit) {