Inputs always crash if workdir contains colon

When running hongfuzz on a trivial `LLVMFuzzerTestOneInput` harness from a directory that contains a `:` like e.g. `foo:bar`, honggfuzz reports all tested inputs as crashes:

The following Dockerfile reproduces the behaviour (on my machines):

```Dockerfile
FROM ubuntu@sha256:35f3a8badf2f74c1b320a643b343536f5132f245cbefc40ef802b6203a166d04
WORKDIR /honggfuzz

RUN apt -y update
RUN apt -y install binutils-dev libunwind-dev libblocksruntime-dev clang make

ADD https://github.com/google/honggfuzz.git#ded8c87bcf3cc32f64c1097746a3461d6da1c24a .
RUN make && make install

COPY <
#include

extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
return 0;
}
EOF

RUN hfuzz-clang++ -fsanitize=fuzzer /harness.cpp -o /harness

COPY <

Start by building honggfuzz with the Dockerfile reproduction and run the entrypoint command from /foo:bar. Trace how honggfuzz handles the workdir and output path when the path contains a colon. Done means the trivial LLVMFuzzerTestOneInput harness no longer reports every tested input as a crash in that environment.

Written by the indexing model from the issue text.