message: fix crash animating with no keyframes
  only happened when hitting spacebar
diff: @@ -260,11 +260,13 @@ MainWindow::MainWindow(StudioCommon &_common)
  activeWindow->frame->child("camera").traverse<sg::PrintNodes>();
  break;
  case GLFW_KEY_SPACE:
  + if (g_camAnchors.size() >= 2) {
  g_animatingPath = !g_animatingPath;
  g_camCurrentPathIndex = 0;
  if (g_animatingPath) {
  g_camPath = buildPath(g_camAnchors, g_camPathSpeed * 0.01);
  }
  + }
  break;
  case GLFW_KEY_EQUAL:
  activeWindow->pushLookMark();
  @@ -1570,10 +1572,9 @@ void MainWindow::buildWindowKeyframes()
  if (ImGui::Button(g_animatingPath ? "stop" : "play")) {
  g_animatingPath = !g_animatingPath;
  g_camCurrentPathIndex = 0;
  - if (g_animatingPath) {
  + if (g_animatingPath)
  g_camPath = buildPath(g_camAnchors, g_camPathSpeed * 0.01);
  }
  - }
  ImGui::SameLine();
  ImGui::SetNextItemWidth(10 * ImGui::GetFontSize());
  ImGui::SliderFloat("speed##path", &g_camPathSpeed, 0.f, 10.0);
  