Apply viewport before SoftwareTransform so flipping can be checked

GPU/Vulkan/DrawEngineVulkan.cpp

@@ -895,6 +895,14 @@ void DrawEngineVulkan::DoFlush() {
 		params.allowSeparateAlphaClear = false;
 		params.provokeFlatFirst = true;
 
+		// We need to update the viewport early because it's checked for flipping in SoftwareTransform.
+		// We don't have a "DrawStateEarly" in vulkan, so...
+		// TODO: Probably should eventually refactor this and feed the vp size into SoftwareTransform directly (Unknown's idea).
+		if (gstate_c.IsDirty(DIRTY_VIEWPORTSCISSOR_STATE)) {
+			gstate_c.vpWidth = gstate.getViewportXScale() * 2.0f;
+			gstate_c.vpHeight = gstate.getViewportYScale() * 2.0f;
+		}
+
 		int maxIndex = indexGen.MaxIndex();
 		SoftwareTransform(
 			prim, indexGen.VertexCount(),