Fix 2008-04-14 regression in asprintf(ptr,"").
* libc/stdio/asnprintf.c (asnprintf, _asnprintf_r): Avoid stdio
baggage.
* libc/stdio/asniprintf.c (asniprintf, _asniprintf_r): Likewise.
* libc/stdio/asiprintf.c (asiprintf, _asiprintf_r): Likewise.
* libc/stdio/vasniprintf.c (_vasniprintf_r): Likewise.
* libc/stdio/vsnprintf.c (_vsnprintf_r): Likewise.
* libc/stdio/vfprintf.c (_VFPRINTF_R) [STRING_ONLY]: Always malloc
an initial buffer for asprintf.