[myanmar] Fix unsafe usage of FLAG_SAFE() The commit f559c633073f63b9d87cb2440048b4413cfa1c05 caused "undefined-shift" errors in Myanmar shaper as we changed the numeric value of type D from 19 to 32 there, making the "FLAG_SAFE (info.myanmar_category())" wrong. Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=3546