fix: Add an early return if login check fails

Previously, even after redirecting to the login activity on failed login
check, the code in the initialize function kept running, eventually
getting to the function that navigates to the calendar activity,
bypassing login.

app/src/main/java/com/p_vacho/neat_calendar/activities/MainActivity.kt

@@ -35,12 +35,13 @@ class MainActivity : AppCompatActivity() {
             // The reachability interceptor will already redirect us to the
             // ApiUnreachableActivity, finish this one.
             finish()
-            return;
+            return
         }
 
         loggedIn = checkUserLogin()
         if (!loggedIn) {
             navigateToLoginActivity()
+            return
         }
 
         navigateToCalendarActivity()