(ITS#8782) Memory leak in ldap_cancel

[cheimes@redhat.com]

Full_Name: Christian Heimes
Version: 2.4.45
OS: Fedora
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (2001:16b8:6097:b200:c324:8c3d:7869:1a1b)


While I was looking for memory leaks in python-ldap, Valgrind detected a memory
leak in ldap_cancel:

==30178== 22 (16 direct, 6 indirect) bytes in 1 blocks are definitely lost in
loss record 27 of 5,810
==30178==    at 0x4C2FB6B: malloc (vg_replace_malloc.c:299)
==30178==    by 0x14CBD9E4: ber_memalloc_x (memory.c:228)
==30178==    by 0x14CBC940: ber_flatten (io.c:437)
==30178==    by 0x14A81733: ldap_cancel (cancel.c:50)
==30178==    by 0x1485A3BA: l_ldap_cancel (LDAPObject.c:779)
==30178==    by 0x4FC24EF: PyCFunction_Call (in
/usr/lib64/libpython3.6m.so.1.0)
==30178==    by 0x4FF891C: _PyEval_EvalFrameDefault (in
/usr/lib64/libpython3.6m.so.1.0)
==30178==    by 0x4F590B2: ??? (in /usr/lib64/libpython3.6m.so.1.0)
==30178==    by 0x4F8BE10: ??? (in /usr/lib64/libpython3.6m.so.1.0)
==30178==    by 0x4FC933D: ??? (in /usr/lib64/libpython3.6m.so.1.0)
==30178==    by 0x4FF2EC9: _PyEval_EvalFrameDefault (in
/usr/lib64/libpython3.6m.so.1.0)
==30178==    by 0x4F590B2: ??? (in /usr/lib64/libpython3.6m.so.1.0)

I think the function is missing a call to ber_bvfree(cancelidvalp).

python-ldap issue: https://github.com/python-ldap/python-ldap/issues/82
Code: https://github.com/openldap/openldap/blob/master/libraries/libldap/cancel.c#L43-L55