Fix crash with combining characters after several cursorRight() calls

cursorRight() does not resize the _screenLines vector, leading to an
assert in QVector when trying to look up the _cuX which is bigger than
the amount of characters in the current line.

BUG: 372530
(cherry picked from commit 80b9e07)

src/Screen.cpp

@@ -640,7 +640,7 @@ void Screen::displayCharacter(unsigned short c)
             return;
         }
         // Find previous "real character" to try to combine with
-        int charToCombineWithX = _cuX;
+        int charToCombineWithX = qMin(_cuX, _screenLines[_cuY].length());
         int charToCombineWithY = _cuY;
         do {
             if (charToCombineWithX > 0) {