SkBlurImageFilter_opt.h: break conditions into separate loops.

This gives ~15% improvement on blur_image on Linux Z620,
and should allow me to implement cropping without
incurring a perf hit.

BUG=skia:
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Review URL: https://codereview.chromium.org/1426583004
1 file changed