ColorPicker: Fix assertion when running in a collapsed window and dragging its title bar (#2389)

docs/CHANGELOG.txt

@@ -54,6 +54,8 @@ Other Changes:
 - InputText: Fixed various display corruption related to swapping the underlying buffer while
   a input widget is active (both for writable and read-only paths). Often they would manifest
   when manipulating the scrollbar of a multi-line input text.
+- ColorPicker: Fixed a bug/assertion when displaying a color picker in a collapsed window
+  while dragging its title bar. (#2389)
 - TabBar: Fixed a crash when using BeginTabBar() recursively (didn't affect docking). (#2371)
 - TabBar: Added extra mis-usage error recovery. Past the assert, common mis-usage don't lead to
   hard crashes any more, facilitating integration with scripting languages. (#1651)

imgui_widgets.cpp

@@ -4219,8 +4219,10 @@ bool ImGui::ColorPicker4(const char* label, float col[4], ImGuiColorEditFlags fl
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = GetCurrentWindow();
-    ImDrawList* draw_list = window->DrawList;
+    if (window->SkipItems)
+        return false;
 
+    ImDrawList* draw_list = window->DrawList;
     ImGuiStyle& style = g.Style;
     ImGuiIO& io = g.IO;