Tables: four small fixes.

Fixed last item flags leaking to disabled column, affecting IsItemHovered(). (#3651).
Validate and fix invalid DisplayOrder data from ini file.
Allow TableHeaderRows() to function will missing TableSetupColumn() calls.
Made TableHeader() use AllowItemOverlap mode to allow submit subsequent item in same cell, since it covers the whole cell area.

imgui.cpp

@@ -4749,6 +4749,7 @@ bool ImGui::IsItemEdited()
 }
 
 // Allow last item to be overlapped by a subsequent item. Both may be activated during the same frame before the later one takes priority.
+// FIXME: Although this is exposed, its interaction and ideal idiom with using ImGuiButtonFlags_AllowItemOverlap flag are extremely confusing, need rework.
 void ImGui::SetItemAllowOverlap()
 {
     ImGuiContext& g = *GImGui;

imgui_tables.cpp

@@ -1369,7 +1369,8 @@ const char* ImGui::TableGetColumnName(int column_n)
 
 const char* ImGui::TableGetColumnName(const ImGuiTable* table, int column_n)
 {
-    IM_ASSERT(table->IsLayoutLocked == true || column_n <= table->DeclColumnsCount); // NameOffset is invalid otherwise
+    if (table->IsLayoutLocked == false && column_n >= table->DeclColumnsCount)
+        return ""; // NameOffset is invalid at this point
     const ImGuiTableColumn* column = &table->Columns[column_n];
     if (column->NameOffset == -1)
         return "";
@@ -1762,7 +1763,6 @@ void ImGui::TableBeginCell(ImGuiTable* table, int column_n)
     window->DC.CursorMaxPos.x = window->DC.CursorPos.x;
     window->DC.ColumnsOffset.x = start_x - window->Pos.x - window->DC.Indent.x; // FIXME-WORKRECT
     window->DC.CurrLineTextBaseOffset = table->RowTextBaseline;
-    window->DC.LastItemId = 0;
     window->DC.NavLayerCurrent = (ImGuiNavLayer)column->NavLayerCurrent;
 
     window->WorkRect.Min.y = window->DC.CursorPos.y;
@@ -1775,6 +1775,12 @@ void ImGui::TableBeginCell(ImGuiTable* table, int column_n)
         window->DC.CursorPos.y = ImMax(window->DC.CursorPos.y, table->RowPosY2);
 
     window->SkipItems = column->IsSkipItems;
+    if (column->IsSkipItems)
+    {
+        window->DC.LastItemId = 0;
+        window->DC.LastItemStatusFlags = 0;
+    }
+
     if (table->Flags & ImGuiTableFlags_NoClip)
     {
         // FIXME: if we end up drawing all borders/bg in EndTable, could remove this and just assert that channel hasn't changed.
@@ -2638,8 +2644,10 @@ void ImGui::TableHeader(const char* label)
     //GetForegroundDrawList()->AddRect(cell_r.Min, cell_r.Max, IM_COL32(255, 0, 0, 255)); // [DEBUG]
     //GetForegroundDrawList()->AddRect(bb.Min, bb.Max, IM_COL32(255, 0, 0, 255)); // [DEBUG]
 
+    // Using AllowItemOverlap mode because we cover the whole cell, and we want user to be able to submit subsequent items.
     bool hovered, held;
-    bool pressed = ButtonBehavior(bb, id, &hovered, &held, ImGuiButtonFlags_None);
+    bool pressed = ButtonBehavior(bb, id, &hovered, &held, ImGuiButtonFlags_AllowItemOverlap);
+    SetItemAllowOverlap();
     if (hovered || selected)
     {
         const ImU32 col = GetColorU32(held ? ImGuiCol_HeaderActive : hovered ? ImGuiCol_HeaderHovered : ImGuiCol_Header);
@@ -3025,6 +3033,7 @@ void ImGui::TableLoadSettings(ImGuiTable* table)
 
     // Serialize ImGuiTableSettings/ImGuiTableColumnSettings into ImGuiTable/ImGuiTableColumn
     ImGuiTableColumnSettings* column_settings = settings->GetColumnSettings();
+    ImU64 display_order_mask = 0;
     for (int data_n = 0; data_n < settings->ColumnsCount; data_n++, column_settings++)
     {
         int column_n = column_settings->Index;
@@ -3044,12 +3053,19 @@ void ImGui::TableLoadSettings(ImGuiTable* table)
             column->DisplayOrder = column_settings->DisplayOrder;
         else
             column->DisplayOrder = (ImGuiTableColumnIdx)column_n;
+        display_order_mask |= (ImU64)1 << column->DisplayOrder;
         column->IsEnabled = column->IsEnabledNextFrame = column_settings->IsEnabled;
         column->SortOrder = column_settings->SortOrder;
         column->SortDirection = column_settings->SortDirection;
     }
 
-    // FIXME-TABLE: Need to validate .ini data
+    // Validate and fix invalid display order data
+    const ImU64 expected_display_order_mask = (settings->ColumnsCount == 64) ? ~0 : ((ImU64)1 << settings->ColumnsCount) - 1;
+    if (display_order_mask != expected_display_order_mask)
+        for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
+            table->Columns[column_n].DisplayOrder = (ImGuiTableColumnIdx)column_n;
+
+    // Rebuild index
     for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
         table->DisplayOrderToIndex[table->Columns[column_n].DisplayOrder] = (ImGuiTableColumnIdx)column_n;
 }