Fixed initial ScrollbarX decision when no vertical scrollbar is in (#246)

imgui.cpp

@@ -3793,8 +3793,8 @@ bool ImGui::Begin(const char* name, bool* p_opened, const ImVec2& size_on_first_
             }
 
             // Scrollbars
-            window->ScrollbarX = (window->SizeContents.x > window->Size.x - style.ScrollbarSize - window->WindowPadding.x) && !(flags & ImGuiWindowFlags_NoScrollbar) && (flags & ImGuiWindowFlags_HorizontalScrollbar);
             window->ScrollbarY = (window->SizeContents.y > window->Size.y + style.ItemSpacing.y) && !(flags & ImGuiWindowFlags_NoScrollbar);
+            window->ScrollbarX = (window->SizeContents.x > window->Size.x - (window->ScrollbarY ? style.ScrollbarSize : 0.0f) - window->WindowPadding.x) && !(flags & ImGuiWindowFlags_NoScrollbar) && (flags & ImGuiWindowFlags_HorizontalScrollbar);
             window->ScrollbarSizes = ImVec2(window->ScrollbarY ? style.ScrollbarSize : 0.0f, window->ScrollbarX ? style.ScrollbarSize : 0.0f);
 
             // Window background