When the table is turned on normalize, the first region may not be merged even the size is 0

Suppose a table has 8 regions, the sizes are [0, 10, 1, 0, 9, 0, 12, 0], the average region size is 4, and split is disabled.

The current Normalizer can only get three merge plans (use size to represent region):

[1, 0], [9, 0],[12, 0]

It can not merge the first region, even it's size is 0.