Improve focusing the filter line with keyboard shortcut

See issue #3439

src/FilterTableHeader.cpp

@@ -137,3 +137,9 @@ QString FilterTableHeader::filterValue(size_t column) const
 {
     return filterWidgets[column]->text();
 }
+
+void FilterTableHeader::setFocusColumn(size_t column)
+{
+    if(column < filterWidgets.size())
+        filterWidgets.at(column)->setFocus();
+}

src/FilterTableHeader.h

@@ -16,7 +16,8 @@ public:
     QSize sizeHint() const override;
     bool hasFilters() const {return (filterWidgets.size() > 0);}
     QString filterValue(size_t column) const;
-    
+    void setFocusColumn(size_t column);
+
 public slots:
     void generateFilters(size_t number, size_t number_of_hidden_filters = 1);
     void adjustPositions();

src/TableBrowser.cpp

@@ -363,7 +363,22 @@ TableBrowser::TableBrowser(DBBrowserDB* _db, QWidget* parent) :
         // Restore cursor because in the ExtendedTableWidget it is changed to a hand when Ctrl+Shift
         // is pressed.
         QApplication::restoreOverrideCursor();
-        ui->dataTable->horizontalHeader()->setFocus();
+        FilterTableHeader* header = qobject_cast<FilterTableHeader*>(ui->dataTable->horizontalHeader());
+        // Set the focus to the current column if valid, otherwise, set focus to the first visible
+        // column.
+        if(!header) {
+            ui->dataTable->horizontalHeader()->setFocus();
+        } else if(currentIndex().isValid()) {
+            header->setFocusColumn(static_cast<size_t>(currentIndex().column()));
+        } else {
+            for(int col = 0; col < ui->dataTable->model()->columnCount(); col++)
+            {
+                if(!ui->dataTable->isColumnHidden(col)) {
+                    header->setFocusColumn(static_cast<size_t>(col));
+                    break;
+                }
+            }
+        }
     });
 
     QShortcut* shortcutActionGlobalFilter = new QShortcut(QKeySequence("Ctrl+Alt+F"), this, nullptr, nullptr, Qt::WidgetWithChildrenShortcut);