Fix GL debugging

The GL debugging isn't working for me at all.

Apparently glGenTextures and friends don't actually create the texture but only reserve a name for them, so labelling them needs to wait until after they have been initialized (which will actually create a texture).

The commit limiting the label length is probably correct but wasn't necessary for me, it's just that the GL docs suck.

After those two, I still get warnings at runtime, but I believe that's a bug in mesa doing a <= 0 instead of a < 0 here: https://gitlab.freedesktop.org/mesa/mesa/blob/master/src/mesa/main/debug_output.c#L1248

So, as always, everything is broken.