don't claim "no move" when search interrupted

I *think* the reason I'm occasionally seeing toasts about not finding a
move is that when the engine's interrupted by there being a UI event in
the queue that error is posted. Instead try posting only when at the end
of the search nothing's been found.

xwords4/android/app/src/main/java/org/eehouse/android/xw4/jni/JNIThread.java

@@ -266,15 +266,19 @@ public class JNIThread extends Thread {
     }
 
     public boolean busy()
-    {                           // synchronize this!!!
+    {
         boolean result = false;
+
+        // Docs: The returned iterator is a "weakly consistent" iterator that
+        // will never throw ConcurrentModificationException, and guarantees to
+        // traverse elements as they existed upon construction of the
+        // iterator, and may (but is not guaranteed to) reflect any
+        // modifications subsequent to construction.
         Iterator<QueueElem> iter = m_queue.iterator();
-        while ( iter.hasNext() ) {
+        while ( iter.hasNext() && !result ) {
-            if ( iter.next().m_isUIEvent ) {
+            result = iter.next().m_isUIEvent;
-                result = true;
-                break;
-            }
         }
+
         return result;
     }
 

xwords4/common/board.c

@@ -2128,13 +2128,13 @@ board_requestHint( BoardCtxt* board,
             result = nTiles > 0;
         }
 
+        XP_Bool canMove = XP_FALSE;
         if ( result ) {
 #ifdef XWFEATURE_SEARCHLIMIT
             BdHintLimits limits;
             BdHintLimits* lp = NULL;
 #endif
             XP_Bool wasVisible;
-            XP_Bool canMove;
 
             wasVisible = setArrowVisible( board, XP_FALSE );
 
@@ -2196,7 +2196,7 @@ board_requestHint( BoardCtxt* board,
             }
         }
 
-        if ( !result ) {
+        if ( !canMove ) {
             util_userError( board->util, ERR_NO_HINT_FOUND );
         }
     }

xwords4/common/engine.c

@@ -528,7 +528,7 @@ engine_findMove( EngineCtxt* engine, const ModelCtxt* model,
                 newMove->nTiles = 0;
                 canMove = XP_FALSE;
             }
-            result = XP_TRUE;
+            XP_ASSERT( result );
         }
 
         util_engineStopping( engine->util );