GPU: Update display after loading state

Fixes black frame after switching renderers.

src/core/gpu.cpp

@@ -140,6 +140,7 @@ bool GPU::DoState(StateWrapper& sw)
     std::vector<u16> vram;
     sw.Do(&vram);
     UpdateVRAM(0, 0, VRAM_WIDTH, VRAM_HEIGHT, vram.data());
+    UpdateDisplay();
   }
   else
   {

src/core/gpu_hw_opengl.cpp

@@ -71,6 +71,7 @@ void GPU_HW_OpenGL::UpdateResolutionScale()
 
   CreateFramebuffer();
   CompilePrograms();
+  UpdateDisplay();
 }
 
 void GPU_HW_OpenGL::DrawRendererStatsWindow()