monitor: Don't rearrange clients if monitor doesn't need redrawing

monitor: Don't rearrange clients if monitor doesn't need redrawing

The monitor_redraw() function unconditionally rearranges the visible
clients when it is called. However, if redrawing was not explicitly
requested, this is not necessary.
This commit changes the monitor_redraw() function not to rearrange
clients if a redraw is not necessary, so that only the status bar
and indicators will be redrawn.