Vulkan: Don't invalidate internal state in InvalidateCachedState

The VULKAN_InvalidateCachedState() function seems to be meant to
invalidate any _cached_ state, i.e. global state of the API which may
have been modified outside the renderer.

However, at the moment, the Vulkan renderer also resets a number of
internal variables which track buffers, offsets, etc, in use. As a
result, the renderer can get into an inconsistant state and/or lose
data.

For example, if VULKAN_InvalidateCachedState() is called in between two
calls to VULKAN_UpdateVertexBuffer(), the data from the first call will
be overwritten by that from the second, as the number of the next vertex
buffer to use will be reset to 0. This can result in rendering errors,
as the same vertex data is used incorrectly for several calls.

By no longer resetting this 'internal' state here, those glitches
disappear. However, I haven't tested this with any applications which
mix the Vulkan renderer with their own Vulkan code (do any such
applications exist?), so this may be insufficient in case a full flush
of the renderer state  -- and possibly a wait on the appropriate fence
-- could be required.

Signed-off-by: David Gow <david@ingeniumdigital.com>

src/render/vulkan/SDL_render_vulkan.c

@@ -3372,11 +3372,7 @@ static void VULKAN_InvalidateCachedState(SDL_Renderer *renderer)
 {
     VULKAN_RenderData *rendererData = (VULKAN_RenderData *)renderer->driverdata;
     rendererData->currentPipelineState = NULL;
-    rendererData->currentVertexBuffer = 0;
-    rendererData->issueBatch = SDL_FALSE;
     rendererData->cliprectDirty = SDL_TRUE;
-    rendererData->currentDescriptorSetIndex = 0;
-    rendererData->currentConstantBufferOffset = 0;
 }
 
 static int VULKAN_RunCommandQueue(SDL_Renderer *renderer, SDL_RenderCommand *cmd, void *vertices, size_t vertsize)