vk_rasterizer: Skip transform feedbacks when extension is unavailable

Avoids calling transform feedback procedures when
VK_EXT_transform_feedback is not available.

src/video_core/renderer_vulkan/vk_rasterizer.cpp

@@ -838,6 +838,10 @@ void RasterizerVulkan::BeginTransformFeedback() {
     if (regs.tfb_enabled == 0) {
         return;
     }
+    if (!device.IsExtTransformFeedbackSupported()) {
+        LOG_ERROR(Render_Vulkan, "Transform feedbacks used but not supported");
+        return;
+    }
 
     UNIMPLEMENTED_IF(regs.IsShaderConfigEnabled(Maxwell::ShaderProgram::TesselationControl) ||
                      regs.IsShaderConfigEnabled(Maxwell::ShaderProgram::TesselationEval) ||
@@ -866,6 +870,9 @@ void RasterizerVulkan::EndTransformFeedback() {
     if (regs.tfb_enabled == 0) {
         return;
     }
+    if (!device.IsExtTransformFeedbackSupported()) {
+        return;
+    }
 
     scheduler.Record(
         [](vk::CommandBuffer cmdbuf) { cmdbuf.EndTransformFeedbackEXT(0, 0, nullptr, nullptr); });