Merge a few additional X509error(ERR_R_MALLOC_FAILURE) calls

Merge a few additional X509error(ERR_R_MALLOC_FAILURE) calls
and various style improvements from the OpenSSL 1.1.1 branch,
which is still under a free license.

- No need to #include <openssl/lhash.h>.
- BUF_MEM_free(3) and sk_pop_free(3) can handle NULL.
- sk_value(3) can handle -1.
- Test pointers with "== NULL" rather than with "!".
- Use the safer "p = malloc(sizeof(*p))" idiom.
- return is not a function.
- Delete very wrong commented out code.

Including parts of the these commits from the 2015 to 2018 time range:
25aaa98a b4faea50 90945fa3 f32b0abe 26a7d938 7fcdbd83 208056b2 5b37fef0

Requested by and OK tb@.