Fix error handling in R_ParseSpawnVars

When R_GetEntityToken returns qfalse it resets pointer for parsing, by
R_ParseSpawnVars not returning qfalse it could cause an infinite loop.

Also add newlines to printfs.
Don't say cubemap is outside lightgrid 6 times
Fix R_GetEntityToken ending prematurely

If spawn var key or value is "" it caused R_GetEntityToken (available to
cgame, used by opengl2) to stop parsing, whereas game VM would continue.

Changed it to match parsing used for game VM
(see G_GET_ENTITY_TOKEN in code/server/sv_game.c).

The map poq3dm5 has a "wait" key with value "".