Backport of https://github.com/snes9xgit/snes9x/commit/5449e2d3c549c172f0e81397a9f2be19b800f902
Fix Vulkan compilation errors.
--- a/vulkan/vulkan_context.cpp
+++ b/vulkan/vulkan_context.cpp
@@ -224,27 +224,33 @@ bool Context::init_device(int preferred_device)
     };
 
     auto device_list = instance->enumeratePhysicalDevices().value;
-    physical_device = nullptr;
+    bool device_chosen = false;
+    physical_device = vk::PhysicalDevice();
 
     if (preferred_device > -1 &&
         (size_t)preferred_device < device_list.size() &&
         check_extensions(required_extensions, device_list[preferred_device]))
     {
         physical_device = device_list[preferred_device];
+        device_chosen = true;
     }
 
-    if (physical_device == nullptr)
+    if (!device_chosen)
     {
         for (auto &device : device_list)
         {
             if (check_extensions(required_extensions, device))
             {
                 physical_device = device;
+                device_chosen = true;
                 break;
             }
         }
     }
 
+    if (!device_chosen)
+        return false;
+
     auto extension_properties = physical_device.enumerateDeviceExtensionProperties().value;
     physical_device.getProperties(&physical_device_props);
 
--- a/vulkan/vulkan_pipeline_image.cpp
+++ b/vulkan/vulkan_pipeline_image.cpp
@@ -1,3 +1,5 @@
+#include <cassert>
+
 #include "vulkan_pipeline_image.hpp"
 #include "slang_helpers.hpp"
 
--- a/vulkan/vulkan_shader_chain.cpp
+++ b/vulkan/vulkan_shader_chain.cpp
@@ -1,3 +1,5 @@
+#include <cassert>
+
 #include "vulkan_shader_chain.hpp"
 #include "slang_helpers.hpp"
 #include "stb_image.h"
--- a/vulkan/vulkan_texture.cpp
+++ b/vulkan/vulkan_texture.cpp
@@ -1,3 +1,5 @@
+#include <cassert>
+
 #include "vulkan_texture.hpp"
 #include "vulkan/vulkan_enums.hpp"
 #include "slang_helpers.hpp"