vulkan: move StreamBuffer frame management to StreamBuffer implementation

Fixes crashes with lots of auto-batched draws in a frame.

src/modules/graphics/vulkan/StreamBuffer.h

@@ -61,7 +61,7 @@ private:
 	VmaAllocation allocation;
 	VmaAllocationInfo allocInfo;
 	VkBuffer buffer = VK_NULL_HANDLE;
-	size_t usedGPUMemory;
+	int frameIndex = 0;
 
 };