Analysis: There were two kinds of failing tests on buildbot with UBSAN.
1) runtime error: signed integer overflow and
2) runtime error: load of value is not valid value for type
Signed integer overflow was occuring because addition of two integers
(size of json array + item number in array) was causing overflow in
json_path_parts_compare. This overflow happens because a->n_item_end
wasn't set.
The second error was occuring because c_path->p.types_used is not
initialized but the value is used later on to check for negative path index.
Fix: For signed integer overflow, use a->n_item_end only in case of range
so that it is set.