Fix build with IMGUI_DISABLE_DEMO_WINDOWS
diff --git a/imgui.cpp b/imgui.cpp
index d977324..0ea284a 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -10910,7 +10910,9 @@
     }
 }
 
+#ifndef IMGUI_DISABLE_DEMO_WINDOWS
 namespace ImGui { void ShowFontAtlas(ImFontAtlas* atlas); }
+#endif
 
 void ImGui::ShowMetricsWindow(bool* p_open)
 {
@@ -11115,12 +11117,14 @@
     }
 
     // Details for Fonts
+#ifndef IMGUI_DISABLE_DEMO_WINDOWS
     ImFontAtlas* atlas = g.IO.Fonts;
     if (TreeNode("Fonts", "Fonts (%d)", atlas->Fonts.Size))
     {
         ShowFontAtlas(atlas);
         TreePop();
     }
+#endif
 
     // Details for Docking
 #ifdef IMGUI_HAS_DOCK