Fuzz introspector: fuzz-bus-label

Fuzzer calltree

0 LLVMFuzzerTestOneInput [function] [call site2] [calltree idx: 00000]
1 bus_label_unescape_n [call site2] [calltree idx: 00001]
1 log_assert_failed [call site2] [calltree idx: 00002]
1 bus_label_escape [call site2] [calltree idx: 00003]
1 log_assert_failed [call site2] [calltree idx: 00004]
1 freep [function] [call site2] [calltree idx: 00005]