Fix #1031: Add range check for log2_parallel_merge_level_minus2.
In the VVC draft, The value of log2_parallel_merge_level_minus2 shall be in the range of 0 to CtbLog2SizeY − 2, inclusive. In the current VTM, it's allowed to have log2_parallel_merge_level_minus2 larger than CtbLog2SizeY − 2.
Edited by Xiang Li