LazReport: check variable existence before trying to show its composition (variables editor form), from Michel Tournay, Issue 26281

git-svn-id: http://svn.freepascal.org/svn/lazarus/branches/fixes_1_2@45491 4005530d-fff6-0310-9dd1-cebe43e6787f
LazReport: implements Zoom in/out using CTRL+MouseWheel, from Michel Tournay, Issue #0026280

git-svn-id: http://svn.freepascal.org/svn/lazarus/branches/fixes_1_2@45492 4005530d-fff6-0310-9dd1-cebe43e6787f