svace fixes: insufficient error handling

svace fixes: insufficient error handling

This commit brings fixes for folowing SVACE-reported issues:

    * UNCHECKED_FUNC_RES.FREAD: Return value of fread function was compared to zero at crash-stack.c:836, but ferror/feof wasn't called.
      Result was compared with zero at /home/abuild/rpmbuild/BUILD/crash-worker-1.0.1/src/crash-stack/crash-stack.c:836

    * HANDLE_LEAK: The handle 'fd' was created at crash-manager.c:508 by calling function 'open' and lost at crash-manager.c:515.
      [acquire] Call of open at /home/abuild/rpmbuild/BUILD/crash-worker-1.0.1/src/crash-manager/crash-manager.c:508
      [leaked] leaked at /home/abuild/rpmbuild/BUILD/crash-worker-1.0.1/src/crash-manager/crash-manager.c:515

    * DEREF_OF_NULL.CONST: Pointer '&tail->next', which was assigned NULL value at crash-stack.c:642, is dereferenced at crash-stack.c:692.
      [dereference] Variable '&tail->next' is dereferenced at /home/abuild/rpmbuild/BUILD/crash-worker-1.0.1/src/crash-stack/crash-stack.c:692
      [null] Assign null at /home/abuild/rpmbuild/BUILD/crash-worker-1.0.1/src/crash-stack/crash-stack.c:642

    * RACE.NO_UMASK: Function 'umask(077)' needs to be called before 'mkstemp' at crash-stack.c:964, to prevent a potential race condition vulnerability.
      function call at /home/abuild/rpmbuild/BUILD/crash-worker-1.0.1/src/crash-stack/crash-stack.c:964

Change-Id: Ief6dd93ec8d795fccffbc2d823a6af8fcf63c965