Count unconfigured blocks from 1 not 0

In the list of unconfigured adsense_managed blocks, it is better to display the number counting from 1 to max, instead of from 0 to max-1. This is easier for managers with a non-php background to understand, because if they specify five blocks, they expect them to be numbered 1 to 5. Then when some but not all of the blocks have been configured you can more easily understand what the remaining ones are. For example, you configure three out of the five blocks, then later you see blocks 3 and 4 unconfigured and think 'I am sure I did three blocks but it now says block 3 is unconfigured'.

The change I have made only alters the text shown, it does not alter the way the array is stored internally.