Rare segfault in Text::drawImplementationSinglePass fixed: _textureGl…

[valid-ptr]

…yphQuadMap[glyphTexture] can exist but it's _primitive can be invalid.

GlyphQuads's interface need to be changed (osg::Referenced now, setupPrimitives() method without definition deleted); TextureGlyphQuadMap changed. Intersection with Text improved (no dynamic_casts, less code)