fix index buffer binding offset

+minor cleanup

Author: megai2

src/imgui_impl_dx9_custom.cpp

@@ -121,9 +121,9 @@ class d912pxy_renderer
 			lastOffset = 0;
 		}
 
-		int getOffset()
+		int getBindingOffset()
 		{
-			return activeOffset * sizeof(Element);
+			return lastOffset;
 		}
 
 		void onFrameEnd()
@@ -198,9 +198,8 @@ class d912pxy_renderer
 				vstream = createVStream<VStreamType>(size);
 				activeOffset = 0;
 			}
-
-			int writeSize = sizeof(Element) * count;			
-			if (vstream->Lock(getOffset(), writeSize, (void**)elements, D3DLOCK_DISCARD) < 0)
+			
+			if (vstream->Lock(activeOffset * sizeof(Element), sizeof(Element) * count, (void**)elements, D3DLOCK_DISCARD) < 0)
 			{
 				doLocalFatal("vstream lock failed");
 				return;
@@ -353,7 +352,7 @@ class d912pxy_renderer
 	{
 		// Render command lists
 		int vtx_offset = 0;
-		int idx_offset = 0;
+		int idx_offset = ib.getBindingOffset();
 		for (int n = 0; n < draw_data->CmdListsCount; n++)
 		{
 			const ImDrawList* cmd_list = draw_data->CmdLists[n];