The find_backtraces() function uses a very convoluted loop to
read the log file. The loop fails to terminate if the last thing
in the log file is the backtrace, since the loop termination condition
(`not line`) continues to be true.
It's not clear why this did not reliably hit before, but it now
reliably reproduces for me on both x86 and aarch64. Perhaps timing
changed, or perhaps previously we had more text on the log.
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