fetchmail -- potential crash in -v -v verbose mode

Matthias Andree reports:

Gunter Nau reported fetchmail crashing on some messages; further
debugging by Petr Uzel and Petr Cerny at Novell/SUSE Czech Republic
dug up that this happened when fetchmail was trying to print, in
-v -v verbose level, headers exceeding 2048 bytes. In this
situation, fetchmail would resize the buffer and fill in further
parts of the message, but forget to reinitialize its va_list
typed source pointer, thus reading data from a garbage address found
on the stack at addresses above the function arguments the caller
passed in; usually that would be the caller’s stack frame.