Fix contentInvalidateAll NPE

 Bug: 5220835
 It is possible to call setProperty before webcore has initialized.
 In that case, the content invalidate is unnecessary as there is no
 content to invalidate, so just ignore the request.

Change-Id: I52471a1739443ba8f1e514a5908678552246d80b
diff --git a/core/java/android/webkit/WebView.java b/core/java/android/webkit/WebView.java
index 6238b72..318e75d 100644
--- a/core/java/android/webkit/WebView.java
+++ b/core/java/android/webkit/WebView.java
@@ -9120,7 +9120,9 @@
 
     /** @hide send content invalidate */
     protected void contentInvalidateAll() {
-        mWebViewCore.sendMessage(EventHub.CONTENT_INVALIDATE_ALL);
+        if (mWebViewCore != null && !mBlockWebkitViewMessages) {
+            mWebViewCore.sendMessage(EventHub.CONTENT_INVALIDATE_ALL);
+        }
     }
 
     /** @hide call pageSwapCallback upon next page swap */