Sheet: enable Split action only if only one merged cell is selected

Both main menu and context menu
 Partially fixes #6744

src/Mod/Spreadsheet/Gui/Command.cpp

@@ -162,7 +162,10 @@ bool CmdSpreadsheetSplitCell::isActive()
             Sheet * sheet = sheetView->getSheet();
 
             if (current.isValid())
-                return sheet->isMergedCell(CellAddress(current.row(), current.column()));
+            {
+                return (sheetView->selectedIndexesRaw().size() == 1 &&
+                    sheet->isMergedCell(CellAddress(current.row(), current.column())));
+            }
         }
     }
     return false;

src/Mod/Spreadsheet/Gui/SheetTableView.cpp

@@ -274,6 +274,11 @@ std::vector<Range> SheetTableView::selectedRanges() const
     return result;
 }
 
+QModelIndexList SheetTableView::selectedIndexesRaw() const
+{
+    return selectedIndexes();
+}
+
 void SheetTableView::insertRows()
 {
     assert(sheet != nullptr);
@@ -966,7 +971,8 @@ void SheetTableView::contextMenuEvent(QContextMenuEvent *)
         actionCut->setEnabled(true);
         actionCopy->setEnabled(true);
         actionDel->setEnabled(true);
-        actionSplit->setEnabled(true);
+        actionSplit->setEnabled(selectedIndexes().size() == 1 &&
+            sheet->isMergedCell(CellAddress(currentIndex().row(),currentIndex().column())));
         actionMerge->setEnabled(true);
     }
 

src/Mod/Spreadsheet/Gui/SheetTableView.h

@@ -58,6 +58,7 @@ public:
     void edit(const QModelIndex &index);
     void setSheet(Spreadsheet::Sheet *_sheet);
     std::vector<App::Range> selectedRanges() const;
+    QModelIndexList selectedIndexesRaw() const;
     QString toHtml() const;
 
 public Q_SLOTS:

src/Mod/Spreadsheet/Gui/SpreadsheetView.cpp

@@ -483,6 +483,11 @@ QModelIndexList SheetView::selectedIndexes() const
     return ui->cells->selectionModel()->selectedIndexes();
 }
 
+QModelIndexList SheetView::selectedIndexesRaw() const
+{
+    return ui->cells->selectedIndexesRaw();
+}
+
 void SpreadsheetGui::SheetView::select(App::CellAddress cell, QItemSelectionModel::SelectionFlags flags)
 {
     ui->cells->selectionModel()->select(model->index(cell.row(), cell.col()), flags);

src/Mod/Spreadsheet/Gui/SpreadsheetView.h

@@ -81,6 +81,7 @@ public:
     std::vector<App::Range> selectedRanges() const;
 
     QModelIndexList selectedIndexes() const;
+    QModelIndexList selectedIndexesRaw() const;
 
     void select(App::CellAddress cell, QItemSelectionModel::SelectionFlags flags);