Limit objc dependency. Fix maximize issue.

setup.cfg

@@ -38,7 +38,7 @@ install_requires =
   keyring
   apscheduler
   sentry-sdk
-  pyobjc-framework-Cocoa
+  pyobjc-framework-Cocoa; sys_platform == 'darwin'
 tests_require =
   pytest
   pytest-qt

src/vorta/notifications.py

@@ -25,7 +25,8 @@ class DarwinNotifications(VortaNotifications):
         notification.setTitle_(title)
         notification.setInformativeText_(text)
         center = NSUserNotificationCenter.defaultUserNotificationCenter()
-        center.deliverNotification_(notification)
+        if center is not None:  # Only works when run from app bundle.
+            center.deliverNotification_(notification)
 
 
 class LinuxNotifications(VortaNotifications):