Fixed VK_ERROR_UNKNOWN -> VK_ERROR_UNKNOWN_COPY

See #385 - thanks @alecazam
diff --git a/include/vk_mem_alloc.h b/include/vk_mem_alloc.h
index 58b233c..50a452f 100644
--- a/include/vk_mem_alloc.h
+++ b/include/vk_mem_alloc.h
@@ -15713,7 +15713,7 @@
     VkBuffer hBuffer,
     const void* pNext)
 {
-    VkResult res = VK_ERROR_UNKNOWN;
+    VkResult res = VK_ERROR_UNKNOWN_COPY;
     switch(hAllocation->GetType())
     {
     case VmaAllocation_T::ALLOCATION_TYPE_DEDICATED:
@@ -15738,7 +15738,7 @@
     VkImage hImage,
     const void* pNext)
 {
-    VkResult res = VK_ERROR_UNKNOWN;
+    VkResult res = VK_ERROR_UNKNOWN_COPY;
     switch(hAllocation->GetType())
     {
     case VmaAllocation_T::ALLOCATION_TYPE_DEDICATED: