libQGLViewer detection is broken

[yurivict]

Without QGLVIEWER_BASE_DIR is begins to build the bundled libQGLViewer.
When QGLVIEWER_BASE_DIR is specified but QGLViewer_LIBRARY_DIR_OTHER isn't, it doesn't build libQGLViewer and just skips the viewer altogether, which doesn't make sense.

Please note that nowadays all systems have libQGLViewer: https://repology.org/metapackage/libqglviewer/versions

Suggested solution: remove the bundled libQGLViewer and require both QGLVIEWER_INCLUDE_DIR and QGLVIEWER_LIB_DIR in order to use the external package.

[ahornung]

Good point. Any chance for a pull request / patch contribution?

[yurivict]

I really don't have resources to fix individual projects that I don't even use.
Normally this is the project maintainers' responsibility.