Scrambler with all zeros on input
Take a look at Figure 49-7 in clause 49:



Idles are type of control code. When sending control codes in a block, you must start the block with a "block type field" to indicate the mix of control and data octets in the block. The value of the block-type field is nonzero. 

Therefore the scrambler will never see a stream of all-zero's, even if idles are sent continuously.