Add default font releaseGLObjects workaround for OSG <3.65

AnyOldName3requested to merge
AnyOldName3-master-patch-00511 into master

This resolves #4704 (closed)

I've not compiled this or anything and I'm going off my memory from around ten or eleven months ago, so if this fails CI or causes more problems, that's why. The most likely issue is that we'll need to make the context current before releasing the program.

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