Add default body

Author: adamint

src/androidMain/kotlin/com/adamratzman/spotify/auth/pkce/AbstractSpotifyPkceLoginActivity.kt

@@ -53,7 +53,7 @@ public abstract class AbstractSpotifyPkceLoginActivity : AppCompatActivity() {
      * Custom logic to invoke when loading begins ([isLoading] is true) or ends ([isLoading] is false).
      * You can update the view here.
      */
-    public open fun setLoadingContent(isLoading: Boolean)
+    public open fun setLoadingContent(isLoading: Boolean) = {}
 
     private lateinit var authorizationIntent: Intent
     private lateinit var credentialStore: SpotifyDefaultCredentialStore