Fix copying one single char

Regression introduced by 5919c1fd.  The selection range is inclusive in
both ends.

Thanks to Chiitoo for reporting and to Yerrey Dev for proposing a
solution.

BUG: 448144

src/Emulation.cpp

@@ -92,7 +92,7 @@ void Emulation::checkScreenInUse()
 
 void Emulation::checkSelectedText()
 {
-    bool isEmpty = _currentScreen->isSelectionEmpty();
+    bool isEmpty = !_currentScreen->hasSelection();
     Q_EMIT selectionChanged(isEmpty);
 }
 

src/Screen.cpp

@@ -1425,15 +1425,6 @@ bool Screen::isSelected(const int x, const int y) const
     return pos >= _selTopLeft && pos <= _selBottomRight && columnInSelection;
 }
 
-bool Screen::isSelectionEmpty() const
-{
-    if (!isSelectionValid()) {
-        return true;
-    }
-
-    return _selTopLeft == _selBottomRight;
-}
-
 QString Screen::selectedText(const DecodingOptions options) const
 {
     if (!isSelectionValid()) {

src/Screen.h

@@ -467,7 +467,6 @@ public:
      */
     bool isSelected(const int x, const int y) const;
 
-    bool isSelectionEmpty() const;
     /**
      * Convenience method.  Returns the currently selected text.
      * @param options See Screen::DecodingOptions