LCL, grids, don't scroll beyond max position, in trunk it only moves scrollbar but grid is without effect, in 1.2.6 this fixes index out of range while scrolling as reported in issue 25862

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@46565 4005530d-fff6-0310-9dd1-cebe43e6787f