Fix crash when scrolling wxGrid in which scrolling is disabled

If "pixels per line" is set to 0, indicating that scrolling is disabled,
just don't scroll in the corresponding direction instead of dividing by
zero.

Closes https://github.com/wxWidgets/wxWidgets/pull/2323

src/generic/grid.cpp

@@ -8099,8 +8099,9 @@ void wxGrid::MakeCellVisible( int row, int col )
          col < -1 || col >= m_numCols )
         return;
 
-    const bool processRow = row != -1;
-    const bool processCol = col != -1;
+    // We don't scroll in the corresponding direction if "pixels per line" is 0.
+    const bool processRow = row != -1 && m_yScrollPixelsPerLine != 0;
+    const bool processCol = col != -1 && m_xScrollPixelsPerLine != 0;
 
     // Get the cell rectangle in logical coords.
     wxRect r;