Update BIT 2D with Range Update and Range Query.cpp

[rishab-nahar]

the previous implementation is incorrect,to duplicate the error give the following input 3 4 6 9 2 1 4 2 5 3 9 1 2 6 2 1 1 1 3 4 -1 2 2 3 3 4

Previous code gives 13,while answer is 12

[ShahjalalShohag]

Thanks a lot!