Avoid bitwise negate of enum value

Fixes this -fno-sanitize-recover=undefined fail,

hb-ot-map.hh:188:1: runtime error: load of value 4294967294, which is not a valid value for type 'hb_ot_map_feature_flags_t'
    #0 0x7f62bfa9b227 in operator&=(hb_ot_map_feature_flags_t&, hb_ot_map_feature_flags_t) /home/ebrahim/Desktop/harfbuzz/src/./hb-ot-map.hh:188:1
    #1 0x7f62bfa9b227 in hb_ot_map_builder_t::compile(hb_ot_map_t&, hb_ot_shape_plan_key_t const&) /home/ebrahim/Desktop/harfbuzz/src/hb-ot-map.cc:194
    #2 0x7f62bface650 in hb_ot_shape_planner_t::compile(hb_ot_shape_plan_t&, hb_ot_shape_plan_key_t const&) /home/ebrahim/Desktop/harfbuzz/src/hb-ot-shape.cc:108:7
    #3 0x7f62bfacec1e in hb_ot_shape_plan_t::init0(hb_face_t*, hb_shape_plan_key_t const*) /home/ebrahim/Desktop/harfbuzz/src/hb-ot-shape.cc:225:11
    #4 0x7f62bfae1318 in hb_shape_plan_create2 /home/ebrahim/Desktop/harfbuzz/src/hb-shape-plan.cc:232:7
    #5 0x7f62bfae1d2a in hb_shape_plan_create_cached2 /home/ebrahim/Desktop/harfbuzz/src/hb-shape-plan.cc:489:33
    #6 0x7f62bfae2527 in hb_shape_full /home/ebrahim/Desktop/harfbuzz/src/hb-shape.cc:135:33
    #7 0x55ed360b6588 in shape_options_t::shape(hb_font_t*, hb_buffer_t*, char const**) /home/ebrahim/Desktop/harfbuzz/util/./options.hh:242:10
    #8 0x55ed360b5d9c in shape_consumer_t<output_buffer_t>::consume_line(char const*, unsigned int, char const*, char const*) /home/ebrahim/Desktop/harfbuzz/util/./shape-consumer.hh:67:19
    #9 0x55ed360b549f in main_font_text_t<shape_consumer_t<output_buffer_t>, 2147483647, 0>::main(int, char**) /home/ebrahim/Desktop/harfbuzz/util/./main-font-text.hh:81:16
    #10 0x55ed360b4e23 in main /home/ebrahim/Desktop/harfbuzz/util/hb-shape.cc:189:17
    #11 0x7f62bf104ee2 in __libc_start_main (/usr/lib/libc.so.6+0x26ee2)
    #12 0x55ed3608f7ad in _start (/home/ebrahim/Desktop/harfbuzz/util/.libs/lt-hb-shape+0xd7ad)
1 file changed