Update imgui (fix issue stack layout / clipping in node with spring)

See ocornut/imgui#846 (comment)

+ sandbox to reproduce the issue

bindings/imgui_bundle/demos_cpp/sandbox/sandbox_stacklayout.cpp

@@ -0,0 +1,57 @@
+#include "imgui.h"
+#include "immapp/immapp.h"
+#include "imgui-node-editor/imgui_node_editor.h"
+
+namespace ed = ax::NodeEditor;
+
+
+void GuiNode()
+{
+    // Basically a vertical layout with 2 inner horizontal layouts that contain text elements + a spring element
+    ImGui::BeginVertical("V");
+    {
+        ImGui::BeginHorizontal("H");
+        {
+            ImGui::Text("Hello");
+            ImGui::Spring();
+            ImGui::Text("world");  // With the new version, this is clipped out!
+        }
+        ImGui::EndHorizontal();
+
+        ImGui::BeginHorizontal("H2");
+        {
+            ImGui::Text("Hello");
+            ImGui::Spring();
+            ImGui::Text("world");
+            ImGui::Text("And again");
+        }
+        ImGui::EndHorizontal();
+    }
+    ImGui::EndVertical();
+}
+
+
+void Gui()
+{
+    // A simple node editor with a single node
+    ed::Begin("Node editor");
+    ed::BeginNode(ed::NodeId(1));
+    {
+        GuiNode();
+    }
+    ed::EndNode();
+    ed::End();
+}
+
+
+int main(int, char**)
+{
+    // Run the application using ImmApp (from ImGui Bundle)
+    // This is simply a way to quickly setup an application with ImGui + Node Editor
+    HelloImGui::RunnerParams runnerParams;
+    runnerParams.callbacks.ShowGui = Gui;
+    ImmApp::AddOnsParams addOnsParams;
+    addOnsParams.withNodeEditor = true;
+    ImmApp::Run(runnerParams, addOnsParams);
+    return 0;
+}

bindings/imgui_bundle/demos_python/sandbox/sandbox_stacklayout.py

@@ -0,0 +1,22 @@
+from imgui_bundle import imgui, immapp, imgui_ctx, imgui_node_editor as ed
+
+
+def gui():
+    with imgui_ctx.begin_vertical("V"):
+        ed.begin("Node editor")
+        ed.begin_node(ed.NodeId(1))
+        with imgui_ctx.begin_horizontal("H"):
+            imgui.text("Hello")
+            imgui.spring()
+            imgui.text("world")
+
+        with imgui_ctx.begin_horizontal("H2"):
+            imgui.text("Hello")
+            imgui.spring()
+            imgui.text("world")
+            imgui.text("And again")
+        ed.end_node()
+        ed.end()
+
+
+immapp.run(gui, with_node_editor=True)