[Toybox] tar xf doesn't work on compressed files if the *cat tools aren't available

[enh]

the kernel folks build in an even more restricted environment than AOSP. so
although they have bzip2 and gzip, they don't have bzcat and gzcat.

from a bad run (with no bzcat/gzcat):

~/aosp-master-with-phones$ /usr/bin/strace -f -e execve
./prebuilts/build-tools/linux-x86/bin/toybox tar tvf x.tar.gz
execve("./prebuilts/build-tools/linux-x86/bin/toybox",
["./prebuilts/build-tools/linux-x8"..., "tar", "tvf", "x.tar.gz"],
0x7ffe8acad930 /* 36 vars */) = 0
/usr/bin/strace: Process 640688 attached
[pid 640688]
execve("/usr/local/google/home/enh/aosp-master-with-phones/prebuilts/build-tools/path/linux-x86/bzip2",
["bzip2", "-d"], 0x7ffd675c2a80 /* 36 vars */) = 0
bzip2: (stdin) is not a bzip2 file.
[pid 640688] +++ exited with 2 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=640688,
si_uid=73769, si_status=2, si_utime=0, si_stime=0} ---
+++ exited with 0 +++

from a successful run (with all the tools):

~/aosp-master-with-phones$ strace -f -e execve
./prebuilts/build-tools/linux-x86/bin/toybox tar tvf x.tar.gz
execve("./prebuilts/build-tools/linux-x86/bin/toybox",
["./prebuilts/build-tools/linux-x8"..., "tar", "tvf", "x.tar.gz"],
0x7ffea9535030 /* 36 vars */) = 0
strace: Process 640431 attached
[pid 640431] execve("/usr/bin/zcat", ["/usr/bin/zcat"], 0x7fffe0fd7580 /*
36 vars */) = 0
[pid 640431] execve("/usr/bin/gzip", ["gzip", "-cd"], 0x55f91049b290 /* 34
vars */) = 0
[pid 640431] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=640431,
si_uid=73769, si_status=0, si_utime=0, si_stime=0} ---
-rw-r----- enh/primarygroup         0  2022-08-25 20:53 foo
+++ exited with 0 +++

there is code to try to use $TOOL -d if the *cat tool doesn't exist (that's
why we're running bzip2 at all), but it's obviously not working here :-(

it also works fine if you explicitly say 'z'.

so here's the setup:

$ touch foo
$ tar czf x.tar.gz foo

here's the failure:

$ tar tf x.tar.gz
bzip2: (stdin) is not a bzip2 file.

here's the success:

$ tar tzf /tmp/x.tar.gz
foo

i didn't get time today to look at this in more detail, but i do notice
that there appears to be an inconsistency between the two ways we choose
the appropriate tool:

    *archiver = FLAG(I) ? TT.I : (FLAG(z) ? "gzip" : (FLAG(J) ?
"xz":"bzip2"));

      struct string_list *zcat = FLAG(I) ? 0 : find_in_path(getenv("PATH"),
        FLAG(j) ? "bzcat" : FLAG(J) ? "xzcat" : "zcat");

is that intentional or a bug?

(i'll try to have another look tomorrow, but since you seem to be nocturnal
atm i thought i'd send this out now anyway :-) )
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