app: [Vulkan] keep VkSurfaceKHR ownership to platforms

Before this change, it was unclear who owned the platform specific
VkSurfaceKHR object, leading to a double-free in the error path for
devices with no Vulkan support. This change moves the ownership to the
platform specific code.

Add vk.EnumeratePhysicalDevices while here (refactor was part of
debugging of the double-free).

Signed-off-by: Elias Naur <mail@eliasnaur.com>

internal/vk/vulkan.go

@@ -816,12 +816,12 @@ func CreateInstance(exts ...string) (Instance, error) {
 		return nil, err
 	}
 	inf := C.VkInstanceCreateInfo{
-		sType:                 C.VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO,
-		enabledExtensionCount: C.uint32_t(len(exts)),
+		sType: C.VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO,
 	}
 	if len(exts) > 0 {
 		cexts := mallocCStringArr(exts)
 		defer freeCStringArr(cexts)
+		inf.enabledExtensionCount = C.uint32_t(len(exts))
 		inf.ppEnabledExtensionNames = &cexts[0]
 	}
 	var inst Instance
@@ -861,17 +861,25 @@ func GetPhysicalDeviceQueueFamilyProperties(pd PhysicalDevice) []QueueFamilyProp
 	return queues
 }
 
-func ChoosePhysicalDevice(inst Instance, surf Surface) (PhysicalDevice, int, error) {
+func EnumeratePhysicalDevices(inst Instance) ([]PhysicalDevice, error) {
 	var count C.uint32_t
 	if err := vkErr(C.vkEnumeratePhysicalDevices(funcs.vkEnumeratePhysicalDevices, inst, &count, nil)); err != nil {
-		return nil, 0, fmt.Errorf("vulkan: vkEnumeratePhysicalDevices: %w", err)
+		return nil, fmt.Errorf("vulkan: vkEnumeratePhysicalDevices: %w", err)
 	}
 	if count == 0 {
-		return nil, 0, errors.New("vulkan: no devices available")
+		return nil, nil
 	}
 	devs := make([]C.VkPhysicalDevice, count)
 	if err := vkErr(C.vkEnumeratePhysicalDevices(funcs.vkEnumeratePhysicalDevices, inst, &count, &devs[0])); err != nil {
-		return nil, 0, fmt.Errorf("vulkan: vkEnumeratePhysicalDevices: %w", err)
+		return nil, fmt.Errorf("vulkan: vkEnumeratePhysicalDevices: %w", err)
+	}
+	return devs, nil
+}
+
+func ChoosePhysicalDevice(inst Instance, surf Surface) (PhysicalDevice, int, error) {
+	devs, err := EnumeratePhysicalDevices(inst)
+	if err != nil {
+		return nil, 0, err
 	}
 	for _, pd := range devs {
 		const caps = C.VK_QUEUE_GRAPHICS_BIT | C.VK_QUEUE_COMPUTE_BIT