use Quartz instead of osacript to detect locked screen on macos

Fixes dschep#168

ntfy/screensaver.py

@@ -97,12 +97,12 @@ def macos_detect():
 
 
 def macos_is_locked():
-    # Strictly-speaking, this detects whether or not the screensaver is running. The screensaver 
-    # may or may not be locked.
-    cmd = '''tell application "System Events"
-                 get running of screen saver preferences
-             end tell'''
-    return check_output([ 'osascript', '-e', cmd ]) == b'true\n'
+    # https: // stackoverflow.com/questions/11505255/osx-check-if-the-screen-is-locked
+    import Quartz
+    d = Quartz.CGSessionCopyCurrentDictionary()
+    screenIsLocked = d.get("CGSSessionScreenIsLocked", 0) == 1
+
+    return screenIsLocked
 
 
 def is_locked():