Guard accessibility function calls

This is a follow up of I2b0ec091a1.

Change-Id: I2801bd1530556cfa6cc176efac9d9f09f2405892
diff --git a/java/src/com/android/inputmethod/keyboard/MainKeyboardView.java b/java/src/com/android/inputmethod/keyboard/MainKeyboardView.java
index e24d4e9..8f79a91 100644
--- a/java/src/com/android/inputmethod/keyboard/MainKeyboardView.java
+++ b/java/src/com/android/inputmethod/keyboard/MainKeyboardView.java
@@ -772,7 +772,9 @@
     }
 
     public void onHideWindow() {
-        mAccessibilityDelegate.onHideWindow();
+        if (AccessibilityUtils.getInstance().isAccessibilityEnabled()) {
+            mAccessibilityDelegate.onHideWindow();
+        }
     }
 
     /**