symcc_fuzzing_helper should handle "No exit code available for afl-showmap" panic gracefully about symcc

[richinseattle]

Backtrace:

[2021-01-25T09:57:23Z INFO  symcc_fuzzing_helper] Running on input /tmp/afl_rar2/secondary/queue/id:002025,src:002019,time:8333074,op:havoc,rep:4,+cov
thread 'main' panicked at 'No exit code available for afl-showmap', src/symcc.rs:368:14
stack backtrace:
   0: rust_begin_unwind
             at /rustc/4253153db205251f72ea4493687a31e04a2a8ca0/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/4253153db205251f72ea4493687a31e04a2a8ca0/library/core/src/panicking.rs:92:14
   2: core::option::expect_failed
             at /rustc/4253153db205251f72ea4493687a31e04a2a8ca0/library/core/src/option.rs:1258:5
   3: symcc_fuzzing_helper::symcc::AflConfig::run_showmap
   4: symcc_fuzzing_helper::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[sebastianpoeplau]

Interesting, I wonder what would cause afl-showmap to terminate without an exit code on a Linux system. Maybe it was killed with a signal? The Rust docs suggest that that might be the reason. Anyway, I agree that it makes sense to skip such cases - they seem to be rare enough.