#12 fix for DIME attachment id autogeneration

[Simon Liddington]

When ids for DIME attachments are generated from
soap.dime_id_format, they all end up with an id of 0.

The patch attached fixes this (but may break some other
cases that the if (id < 0) was supposed to cater for).

It may be the case that id should be -1 at this point
but this is not the case because an id has been got
from soap_element_id() in my case.

A similar patch should be applied to stdsoap2.c and for
all other versions of soap_attachment() for palm etc.

[Simon Liddington]

patch for stdsoap2_cpp.cpp