...to silence a clang-analyzer-deadcode.DeadStores on the last update of nLeft
and nRight, each.  Also, adding a gap of 3 to nRight in case no further buttons
will be layed out next to maDockRect resp. maHideRect is irrelevant, as nRight
will not be used for any further layout computations in those cases.

Change-Id: I251d4470099b1f98782ebdfd0c776d881bb7fae5