Tables: Fixed an issue with ScrollX enabled where an extraneous draw command would be created.

Randomly found while deep-diving into ocornut#6765.
ContentMaxXHeadersUsed has been set to max since the dawn of tables, which contradict the intent of passing zero-width to ItemSize(). The ItemSize code allowed SameLine() to operate, but this mistake setting ContentMaxXHeadersUsed would make right-most visible column in a ScrollX set incorrectly use a draw command due to header claiming whole column width.

Author: ocornut

docs/CHANGELOG.txt

@@ -109,7 +109,8 @@ Other changes:
   - Fixed bottom-most and right-most outer border offset by one. (#6765, #3752) [@v-ein]
   - Fixed top-most outer border being drawn with both TableBorderLight and TableBorderStrong
     in some situations, causing the earlier to be visible underneath when alpha is not 1.0f.
-  - fixed right-clicking right-most section (past right-most column) from highlighting a column.
+  - Fixed right-clicking right-most section (past right-most column) from highlighting a column.
+  - Fixed an issue with ScrollX enabled where an extraneous draw command would be created.
 - TabBar: Fixed position of unsaved document marker (ImGuiTabItemFlags_UnsavedDocument) which was
   accidentally offset in 1.89.9. (#6862) [@alektron]
 - Fonts: 'float size_pixels' passed to AddFontXXX() functions is now rounded to lowest integer.

imgui_tables.cpp

@@ -3015,21 +3015,24 @@ void ImGui::TableHeader(const char* label)
     // Calculate ideal size for sort order arrow
     float w_arrow = 0.0f;
     float w_sort_text = 0.0f;
+    bool sort_arrow = false;
     char sort_order_suf[4] = "";
     const float ARROW_SCALE = 0.65f;
     if ((table->Flags & ImGuiTableFlags_Sortable) && !(column->Flags & ImGuiTableColumnFlags_NoSort))
     {
         w_arrow = ImTrunc(g.FontSize * ARROW_SCALE + g.Style.FramePadding.x);
+        if (column->SortOrder != -1)
+            sort_arrow = true;
         if (column->SortOrder > 0)
         {
             ImFormatString(sort_order_suf, IM_ARRAYSIZE(sort_order_suf), "%d", column->SortOrder + 1);
             w_sort_text = g.Style.ItemInnerSpacing.x + CalcTextSize(sort_order_suf).x;
         }
     }
 
-    // We feed our unclipped width to the column without writing on CursorMaxPos, so that column is still considering for merging.
+    // We feed our unclipped width to the column without writing on CursorMaxPos, so that column is still considered for merging.
     float max_pos_x = label_pos.x + label_size.x + w_sort_text + w_arrow;
-    column->ContentMaxXHeadersUsed = ImMax(column->ContentMaxXHeadersUsed, column->WorkMaxX);
+    column->ContentMaxXHeadersUsed = ImMax(column->ContentMaxXHeadersUsed, sort_arrow ? cell_r.Max.x : ImMin(max_pos_x, cell_r.Max.x));
     column->ContentMaxXHeadersIdeal = ImMax(column->ContentMaxXHeadersIdeal, max_pos_x);
 
     // Keep header highlighted when context menu is open.