Handle negative numbers smaller than -9

Author: markshannon

Tools/cases_generator/stack.py

@@ -64,7 +64,7 @@ def from_item(item: StackItem) -> "PointerOffset":
             if txt[0] == "+":
                 txt = txt[1:]
             if txt[0] == "-":
-                n = (txt[1],)
+                n = (txt[1:],)
             else:
                 p = (txt,)
         return PointerOffset(i, p, n)