Fix bufferIndex check in VulkanWindowContext

tools/viewer/sk_app/VulkanWindowContext.cpp

 
 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrContext.h"
 #include "GrRenderTarget.h"
@@ skipping 394 matching lines @@
 
     fContext->unref();
 
     fBackendContext.reset(nullptr);
 }
 
 VulkanWindowContext::BackbufferInfo* VulkanWindowContext::getAvailableBackbuffer() {
     SkASSERT(fBackbuffers);
 
     ++fCurrentBackbufferIndex;
-    if (fCurrentBackbufferIndex > fImageCount) {
+    if (fCurrentBackbufferIndex >= fImageCount) {
         fCurrentBackbufferIndex = 0;
     }
 
     BackbufferInfo* backbuffer = fBackbuffers + fCurrentBackbufferIndex;
 
     GR_VK_CALL_ERRCHECK(fBackendContext->fInterface,
                         WaitForFences(fBackendContext->fDevice, 2, backbuffer->fUsageFences,
                                       true, UINT64_MAX));
     return backbuffer;
 }
@@ skipping 171 matching lines @@
         1, // swapchainCount
         &fSwapchain, // pSwapchains
         &backbuffer->fImageIndex, // pImageIndices
         NULL // pResults
     };
 
     fQueuePresentKHR(fPresentQueue, &presentInfo);
 }
 
 }   //namespace sk_app