[Fix] using WelsRound for all the double-int32_t conversion

reviewed in https://rbcommons.com/s/OpenH264/r/444/

put all (int32_t) to WELS_ROUND to minimize possible mismatch on double-float calculation on different machines
and remove some unnecessary (int32_t)
what we found is that in two machines the results of a multiplying of double variables turn out to be different.
On the centos tested, when using (int32_t), the problematic area is 24000.00*0.5000 = 11999
On the ubuntu tested, when using (int32_t), the problematic area is 24000.00*0.5000 = 12000
Then this difference result in different target bit rate and then QP difference in MB level.