Reducing the number of recursive calls.
Reducing the number of recursive calls.

Both decode_modes_sb and decode_modes_b had conditions to immediately
return at the beginning. Eliminating these conditions here and calling
these functions only to do a real work. Also unrolling loop for
PARTITION_SPLIT.

Change-Id: I2fc41cb74ac491f045a2f04fe68d30ff4aaa555d

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