Avoid `if` call in the `__parallel_merge_submitter_large::run_parallel_merge()` #260

Job	Run time
clang-format	14s
HOST,bknd=omp,cmplr=clang++,macos-latest,std=c++17,cfg=release	4m 19s
CPU,bknd=dpcpp,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	2m 31s
FPGA_EMU,bknd=dpcpp,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	3m 8s
HOST,bknd=tbb,cmplr=icx-cl,windows-latest,std=c++17,cfg=release	17m 28s
HOST,bknd=tbb,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	12m 8s
HOST,bknd=tbb,cmplr=cl,windows-latest,std=c++17,cfg=release	16m 37s
HOST,bknd=omp,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	9m 43s
HOST,bknd=omp,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	6m 2s
CPU,bknd=dpcpp,cmplr=icx,windows-latest,std=c++17,cfg=release	6m 40s
HOST,bknd=tbb,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	9m 10s
HOST,bknd=tbb,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	9m 8s
HOST,bknd=tbb,cmplr=clang++,ubuntu-latest,std=с++17,cfg=release	11m 20s
HOST,bknd=omp,cmplr=clang++,ubuntu-latest,std=с++17,cfg=release	8m 27s
HOST,bknd=tbb,cmplr=clang++,ubuntu-latest,std=с++17,cfg=release	10m 49s
HOST,bknd=tbb,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	11m 29s
HOST,bknd=serial,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	4m 49s
CPU,bknd=dpcpp,cmplr=icpx,ubuntu-latest,std=с++20,cfg=release	2m 34s
HOST,bknd=tbb,cmplr=icpx,ubuntu-latest,std=с++20,cfg=release	17m 33s
HOST,bknd=omp,cmplr=icpx,ubuntu-latest,std=с++20,cfg=release	17m 58s
	3h 2m 7s

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