stacktool.c sass_id may be used unitialized.

[Michael Wood-Vasey]

stacktool.c: In function ‘main’:
stacktool.c:489: warning: ‘sass_id’ may be used uninitialized in this function
stacktool.c:489: note: ‘sass_id’ was declared here
---
Relevant code snippet is:

---

CZW Add an association entry here.
Define the requested association, and insert it if it doesn't already exist
stackAssociationRow *association = pxStackAssociationDefine(config,stack_id);
psS64 sass_id;
if (!association->sass_id) {

---

I rewrote the above line as

psS64 sass_id = -1;

but I don't know if (a) this is the right initalization. (b) if later the return type for sass_id might change to unsigned long long (psU64) and this will have to be changed to 0. I fear, however, that 0 is a valid value for a sass_id so -1 seemed the better choice for now.