Fix font fallback list on macOS with default family

Even with an empty font family we should produce a font fallback list, and we can.
Fixes the missing checkmark (when not affected by clipping).

sixtyfps_runtime/rendering_backends/gl/fonts.rs

@@ -142,14 +142,14 @@ pub(crate) fn font_fallbacks_for_request(
     _request: &FontRequest,
     _reference_text: &str,
 ) -> Vec<FontRequest> {
-    _request
-        .family
-        .as_ref()
-        .and_then(|family| {
-            core_text::font::new_from_name(&family, _request.pixel_size.unwrap_or_default() as f64)
-                .ok()
-        })
-        .map(|requested_font| {
+    let requested_font = match core_text::font::new_from_name(
+        &_request.family.as_ref().map_or_else(|| "", |s| s.as_str()),
+        _request.pixel_size.unwrap_or_default() as f64,
+    ) {
+        Ok(f) => f,
+        Err(_) => return vec![],
+    };
+
     core_text::font::cascade_list_for_languages(
         &requested_font,
         &core_foundation::array::CFArray::from_CFTypes(&[]),
@@ -164,8 +164,6 @@ pub(crate) fn font_fallbacks_for_request(
     .filter(|fallback| !fallback.family.as_ref().unwrap().starts_with(".")) // font-kit asserts when loading `.Apple Fallback`
     .take(1) // Take only the top from the fallback list until we mmap the llaaarge font files
     .collect::<Vec<_>>()
-        })
-        .unwrap_or_default()
 }
 
 #[cfg(target_os = "windows")]