Prevent out of range magnification scale to be persisted.

1. If a bad magnification scale is persisted, i.e. it is
   not between the min and max, the screen magnifier gets
   into a bad state which even a reboot does not fix since
   the scale is persisted in settings.

   This change ensures that only valid scales are presisted.
   In general a bad value should not be attempted to be
   persisted but at this point this is the safest change.

bug:7288239

Change-Id: I3e9c7c091772fa64128ab8403c2127ce65cb94b8

Author: sganov

services/java/com/android/server/accessibility/ScreenMagnifier.java

@@ -376,7 +376,8 @@ public void onMotionEvent(MotionEvent event) {
             }
             if (event.getActionMasked() == MotionEvent.ACTION_UP) {
                 clear();
-                final float scale = mMagnificationController.getScale();
+                final float scale = Math.min(Math.max(mMagnificationController.getScale(),
+                        MIN_SCALE), MAX_SCALE);
                 if (scale != getPersistedScale()) {
                     persistScale(scale);
                 }