video_core: defensively program around unmapped device pointers

src/video_core/renderer_opengl/present/layer.cpp

@@ -131,10 +131,12 @@ FramebufferTextureInfo Layer::LoadFBToScreenInfo(const Tegra::FramebufferConfig&
     const u64 size_in_bytes{Tegra::Texture::CalculateSize(
         true, bytes_per_pixel, framebuffer.stride, framebuffer.height, 1, block_height_log2, 0)};
     const u8* const host_ptr{device_memory.GetPointer<u8>(framebuffer_addr)};
+    if (host_ptr) {
         const std::span<const u8> input_data(host_ptr, size_in_bytes);
         Tegra::Texture::UnswizzleTexture(gl_framebuffer_data, input_data, bytes_per_pixel,
-                                     framebuffer.width, framebuffer.height, 1, block_height_log2,
-                                     0);
+                                         framebuffer.width, framebuffer.height, 1,
+                                         block_height_log2, 0);
+    }
 
     glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
     glPixelStorei(GL_UNPACK_ROW_LENGTH, static_cast<GLint>(framebuffer.stride));

src/video_core/renderer_vulkan/present/layer.cpp

@@ -270,9 +270,11 @@ void Layer::UpdateRawImage(const Tegra::FramebufferConfig& framebuffer, size_t i
     const u64 linear_size{GetSizeInBytes(framebuffer)};
     const u64 tiled_size{Tegra::Texture::CalculateSize(
         true, bytes_per_pixel, framebuffer.stride, framebuffer.height, 1, block_height_log2, 0)};
+    if (host_ptr) {
         Tegra::Texture::UnswizzleTexture(
             mapped_span.subspan(image_offset, linear_size), std::span(host_ptr, tiled_size),
             bytes_per_pixel, framebuffer.width, framebuffer.height, 1, block_height_log2, 0);
+    }
 
     const VkBufferImageCopy copy{
         .bufferOffset = image_offset,