message: Disable fragment shader when generating shadow map.
  This fixes the following validation warning:
  fragment shader writes to output location 0 with no matching attachment
diff: @@ -755,9 +755,9 @@ public:
  enablePCF = 1;
  VK_CHECK_RESULT(vkCreateGraphicsPipelines(device, pipelineCache, 1, &pipelineCreateInfo, nullptr, &pipelines.sceneShadowPCF));
  - // Offscreen pipeline
  + // Offscreen pipeline (vertex shader only)
  shaderStages[0] = loadShader(getAssetPath() + "shaders/shadowmapping/offscreen.vert.spv", VK_SHADER_STAGE_VERTEX_BIT);
  - shaderStages[1] = loadShader(getAssetPath() + "shaders/shadowmapping/offscreen.frag.spv", VK_SHADER_STAGE_FRAGMENT_BIT);
  + pipelineCreateInfo.stageCount = 1;
  // No blend attachment states (no color attachments used)
  colorBlendState.attachmentCount = 0;
  // Cull front faces
  