[khmer] Reinstate a pause after basic features This was removed as part of 044d7a06db552e1564b8575f4d23798f009d9dde, which caused the regression. Just adding a pause fixes the shaping. Debugged by just tracing the good/bad shaping and observing the lookup orders intermingling in the bad shaping. Test: hb-shape LeelawUI.ttf --unicodes U+1780,U+17D2,U+179A,U+17BB Fixes https://github.com/harfbuzz/harfbuzz/issues/3531