notify BoardCanvas when we're closing a game so that it won't try to

use, in callback on UI thread, a dict that may no longer be valid.
Theory is this is why I'm seeing odd crashes in the jni.

xwords4/android/XWords4/src/org/eehouse/android/xw4/BoardActivity.java

@@ -2095,6 +2095,7 @@ public class BoardActivity extends XWActivity
                 m_jniThread.waitToStop( save );
                 m_jniThread = null;
             }
+            m_view.stopHandling();
 
             clearThis();
 

xwords4/android/XWords4/src/org/eehouse/android/xw4/BoardCanvas.java

@@ -165,10 +165,12 @@ public class BoardCanvas extends Canvas implements DrawCtx {
 
     public void setJNIThread( JNIThread jniThread )
     {
-        if ( ! jniThread.equals( m_jniThread ) ) {
+        DbgUtils.assertOnUIThread();
+        if ( null == jniThread ) {
+        } else if ( ! jniThread.equals( m_jniThread ) ) {
             DbgUtils.logf( "BoardCanvas changing threads" );
-            m_jniThread = jniThread;
         }
+        m_jniThread = jniThread;
     }
 
     public int getCurPlayer()
@@ -538,9 +540,9 @@ public class BoardCanvas extends Canvas implements DrawCtx {
                 m_dictChars = null;
                 m_activity.runOnUiThread( new Runnable() {
                         public void run() {
+                            if ( null != m_jniThread ) {
                                 m_dictChars = XwJNI.dict_getChars( dictPtr );
                                 // draw again
-                            if ( null != m_jniThread ) {
                                 m_jniThread.handle( JNIThread.JNICmd
                                                     .CMD_INVALALL );
                             }

xwords4/android/XWords4/src/org/eehouse/android/xw4/BoardView.java

@@ -269,6 +269,15 @@ public class BoardView extends View implements BoardHandler, SyncedDraw {
         invalidate();
     }
 
+    public void stopHandling()
+    {
+        m_jniThread = null;
+        m_jniGamePtr = 0;
+        if ( null != m_canvas ) {
+            m_canvas.setJNIThread( null );
+        }
+    }
+
     // SyncedDraw interface implementation
     public void doJNIDraw()
     {