Fixed Coverity reported issue.
Fixed Coverity reported issue.

CID 11831: Uninitialized pointer field (UNINIT_CTOR)
Non-static class member _context is not initialized in this constructor nor in any functions that it calls.
Non-static class member _dc is not initialized in this constructor nor in any functions that it calls.
Non-static class member _handle is not initialized in this constructor nor in any functions that it calls.
Non-static class member _instance is not initialized in this constructor nor in any functions that it calls.



openscenegraph/osg,scrawl/osg,scrawl/osg,openscenegraph/osg,artoolkit/osg,marchelbling/osg,artoolkit/osg,tomasthoresen/osg,jtorresfabra/osg,marchelbling/osg,scrawl/osg,marchelbling/osg,jtorresfabra/osg,tomasthoresen/osg,scrawl/osg,jtorresfabra/osg,artoolkit/osg,openscenegraph/osg,tomasthoresen/osg,tomasthoresen/osg,marchelbling/osg,jtorresfabra/osg,openscenegraph/osg,artoolkit/osg