Fix double save when changing extension settings (#19)

handleExtensionChange was calling handleFormChange() explicitly, but the
change event also bubbles up to the form's onchange handler which calls
handleFormChange() again - causing two saves per change.

Now handleExtensionChange only calls checkCacheStatus() since the form's
onchange already handles saving.

src/lib/ConfigurePage.svelte

@@ -182,7 +182,6 @@
     }
 
     function handleExtensionChange() {
-        handleFormChange();
         checkCacheStatus();
     }
 </script>