QwtPlot::canvasMap: margins fixed in case of disabled axes


git-svn-id: svn://svn.code.sf.net/p/qwt/code/branches/qwt-6.1@1972 29e17f8d-cf37-471e-a288-72cc03a76eda
QwtLinearScaleEngine::divideScale: check for intervals > DOUBLE_MAX
added


git-svn-id: svn://svn.code.sf.net/p/qwt/code/branches/qwt-6.1@1976 29e17f8d-cf37-471e-a288-72cc03a76eda