Nav, Docking: Fix crash on dimming docked window and DockSpaceOverViewport() with PassthruCentralNode.

(amend 1dc3af3, 23ef6c1, 657073a)

# Conflicts:
#	imgui.cpp

imgui.cpp

@@ -4456,7 +4456,11 @@ static void ImGui::RenderDimmedBackgroundBehindWindow(ImGuiWindow* window, ImU32
 
     // Draw behind window by moving the draw command at the FRONT of the draw list
     {
+        // We've already called AddWindowToDrawData() which called DrawList->ChannelsMerge() on DockNodeHost windows,
+        // and draw list have been trimmed already, hence the explicit recreation of a draw command if missing.
         ImDrawList* draw_list = window->RootWindow->DrawList;
+        if (draw_list->CmdBuffer.Size == 0)
+            draw_list->AddDrawCmd();
         draw_list->PushClipRect(viewport_rect.Min - ImVec2(1, 1), viewport_rect.Max + ImVec2(1, 1), false); // Ensure ImDrawCmd are not merged
         draw_list->AddRectFilled(viewport_rect.Min, viewport_rect.Max, col);
         ImDrawCmd cmd = draw_list->CmdBuffer.back();
@@ -4512,6 +4516,8 @@ static void ImGui::RenderDimmedBackgrounds()
         bb.Expand(distance);
         if (bb.GetWidth() >= viewport->Size.x && bb.GetHeight() >= viewport->Size.y)
             bb.Expand(-distance - 1.0f); // If a window fits the entire viewport, adjust its highlight inward
+        if (window->DrawList->CmdBuffer.Size == 0)
+            window->DrawList->AddDrawCmd();
         window->DrawList->PushClipRect(viewport->Pos, viewport->Pos + viewport->Size);
         window->DrawList->AddRect(bb.Min, bb.Max, GetColorU32(ImGuiCol_NavWindowingHighlight, g.NavWindowingHighlightAlpha), window->WindowRounding, 0, 3.0f);
         window->DrawList->PopClipRect();

imgui_draw.cpp

@@ -473,6 +473,7 @@ void ImDrawList::_PopUnusedDrawCmd()
 
 void ImDrawList::AddCallback(ImDrawCallback callback, void* callback_data)
 {
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     IM_ASSERT(curr_cmd->UserCallback == NULL);
     if (curr_cmd->ElemCount != 0)
@@ -494,6 +495,7 @@ void ImDrawList::AddCallback(ImDrawCallback callback, void* callback_data)
 // Try to merge two last draw commands
 void ImDrawList::_TryMergeDrawCmds()
 {
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     ImDrawCmd* prev_cmd = curr_cmd - 1;
     if (ImDrawCmd_HeaderCompare(curr_cmd, prev_cmd) == 0 && curr_cmd->UserCallback == NULL && prev_cmd->UserCallback == NULL)
@@ -508,6 +510,7 @@ void ImDrawList::_TryMergeDrawCmds()
 void ImDrawList::_OnChangedClipRect()
 {
     // If current command is used with different settings we need to add a new command
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     if (curr_cmd->ElemCount != 0 && memcmp(&curr_cmd->ClipRect, &_CmdHeader.ClipRect, sizeof(ImVec4)) != 0)
     {
@@ -530,6 +533,7 @@ void ImDrawList::_OnChangedClipRect()
 void ImDrawList::_OnChangedTextureID()
 {
     // If current command is used with different settings we need to add a new command
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     if (curr_cmd->ElemCount != 0 && curr_cmd->TextureId != _CmdHeader.TextureId)
     {
@@ -553,6 +557,7 @@ void ImDrawList::_OnChangedVtxOffset()
 {
     // We don't need to compare curr_cmd->VtxOffset != _CmdHeader.VtxOffset because we know it'll be different at the time we call this.
     _VtxCurrentIdx = 0;
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     //IM_ASSERT(curr_cmd->VtxOffset != _CmdHeader.VtxOffset); // See #3349
     if (curr_cmd->ElemCount != 0)