F3 menu shows block light level for non-spawnable blocks

In previous versions, the block light level value on the F3 screen would read 0 when you're on a block that can't spawn monsters. Now they read normal numbers like a full block. This makes spawn-proofing more difficult since you can't just ignore the places where the block light level is 0, you have to check which blocks are bottom half slabs or other non-spawnable blocks, and which ones aren't.