LibVT: Fix out-of bounds line insert

Unless DECOM mode is enabled, the cursor positions are measured from the
top left corner of the screen. We counted from the top margin, causing
line inserts in `vim` to go out-of-bounds and crash the terminal.

Userland/Libraries/LibVT/Terminal.cpp

@@ -608,7 +608,7 @@ void Terminal::IL(Parameters params)
         count = params[0];
     invalidate_cursor();
     for (; count > 0; --count) {
-        active_buffer().insert(cursor_row() + m_scroll_region_top, make<Line>(m_columns));
+        active_buffer().insert(cursor_row(), make<Line>(m_columns));
         if (m_scroll_region_bottom + 1 < active_buffer().size())
             active_buffer().remove(m_scroll_region_bottom + 1);
         else
@@ -640,7 +640,7 @@ void Terminal::DL(Parameters params)
     count = min(count, max_count);
 
     for (int c = count; c > 0; --c) {
-        active_buffer().remove(cursor_row() + m_scroll_region_top);
+        active_buffer().remove(cursor_row());
         if (m_scroll_region_bottom < active_buffer().size())
             active_buffer().insert(m_scroll_region_bottom, make<Line>(m_columns));
         else