builtin printf's `%b` won't expand null

[Tavis Ormandy]

Machine: i686
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i686'
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i686-pc-linux-gnu'
-DCONF_VENDOR='pc' -DSHELL -DHAVE_CONFIG_H  -I.  -I. -I./include -I./lib
-march=pentium4 -O2 -pipe -w -fomit-frame-pointer
uname output: Linux insomniac 2.6.7 #1 Fri Jul 23 22:03:36 BST 2004 i686
Intel(R) Pentium(R) 4 CPU 1500MHz GenuineIntel GNU/Linux
Machine Type: i686-pc-linux-gnu

Bash Version: 2.05b
Patch Level: 0
Release Status: release

Description:
        
        both of these work:

        $ printf "%c" $'\xff' | hexdump -e '"%#04x\n"'
        0xff
        $ printf "%b" \\xff | hexdump -e '"%#04x\n"'
        0xff
        
        but with 0x00, %c accepts it and %b won't
        $ printf "%c" $'\x00' | hexdump -e '"%#04x\n"'
        0000
        $ printf "%b" \\x00 | hexdump -e '"%#04x\n"'
        $

Repeat-By:
        printf "%b" \\x00 | hexdump -e '"%#04x\n"'

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taviso@sdf.lonestar.org | finger me for my gpg key.
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