Nav: clear navid in NavInitWindow() when window is marked with ImGuiWindowFlags_NoNavInputs. (#787)

(no expected side-effects, maybe consistency, but those NavLastIds[] values would likely have been 0 already)

imgui.cpp

@@ -8916,8 +8916,14 @@ void ImGui::NavInitWindow(ImGuiWindow* window, bool force_reinit)
 {
     ImGuiContext& g = *GImGui;
     IM_ASSERT(window == g.NavWindow);
+
+    if (window->Flags & ImGuiWindowFlags_NoNavInputs)
+    {
+        g.NavId = g.NavFocusScopeId = 0;
+        return;
+    }
+
     bool init_for_nav = false;
-    if (!(window->Flags & ImGuiWindowFlags_NoNavInputs))
     if (window == window->RootWindow || (window->Flags & ImGuiWindowFlags_Popup) || (window->NavLastIds[0] == 0) || force_reinit)
         init_for_nav = true;
     IMGUI_DEBUG_LOG_NAV("[nav] NavInitRequest: from NavInitWindow(), init_for_nav=%d, window=\"%s\", layer=%d\n", init_for_nav, window->Name, g.NavLayer);