*: simplify checks for gz/bz2/xz magic

function                                             old     new   delta
send_tree                                            360     355      -5
rpm2cpio_main                                        249     220     -29
setup_unzip_on_fd                                    150     118     -32
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(add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-66)             Total: -66 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
3 files changed