Fix coverity reports NULL_RETURNS (check if fCanvasImp is not 0).
Fix coverity reports NULL_RETURNS (check if fCanvasImp is not 0).


git-svn-id: ecbadac9c76e8cf640a0bca86f6bd796c98521e3@42669 27541ba8-7e3a-0410-8455-c3a389f83636

bbannier/ROOT,bbannier/ROOT,bbannier/ROOT,bbannier/ROOT,bbannier/ROOT,bbannier/ROOT,bbannier/ROOT