initialize viewMat to fix spurious errors when setting view before init()

Author: nmwsharp

include/polyscope/context.h

@@ -88,7 +88,7 @@ struct Context {
   double nearClipRatio = view::defaultNearClipRatio;
   double farClipRatio = view::defaultFarClipRatio;
   std::array<float, 4> bgColor{{1.0, 1.0, 1.0, 0.0}};
-  glm::mat4x4 viewMat;
+  glm::mat4x4 viewMat{std::numeric_limits<float>::quiet_NaN()};
   double fov = view::defaultFov;
   ProjectionMode projectionMode = ProjectionMode::Perspective;
   glm::vec3 viewCenter;

include/polyscope/view.h

@@ -177,6 +177,7 @@ void updateFlight();
 // It is set to invalid initially, but we call ensureViewValid() before any renders.
 // This ensures we never try to render with an invalid view, but also allows the user to
 // set custom views if they wish, without them getting overwritten.
+bool viewIsValid();
 void invalidateView();
 void ensureViewValid();