Fix sparse vectors eadd on CPU

[vkutuev]

Short description

Replace absent vectors' elements with corresponding fill_value in sparse to sparse vectors ewiseadd operation on CPU

List of changes

Fix implementation of src/cpu/cpu_v_eadd.hpp:spla::Algo_v_eadd_cpu::execute_spNsp

Type of changes

• bug-fix (change which fixes Vector: sparse ewiseadd bug (cpu) #229 )
• new-feature (change which proposes new feature or functionality)
• breaking-change (change which brakes compatibility of api or etc.)

Testing strategy

Run vector tests without OpenCL accelerators:

• Replace SPLA_GTEST_MAIN_WITH_FINALIZE_PLATFORM(0) in tests/test_vector.cpp:500
  with SPLA_GTEST_MAIN_WITH_FINALIZE_NO_ACC()
• Rebuild project
• Run tests

Now test vector.eadd_sub_pow2 works fine on CPU