games/holotz-castle: unbreak with clang 4.0

JLib/Util/JTextFile.cpp:148:11: error: ordered comparison between pointer and zero ('s8 *'

    (aka 'char *') and 'int')
if (tmp > 0)
    ~~~ ^ ~

JLib/Util/JTextFile.cpp:156:15: error: ordered comparison between pointer and zero ('s8 *'

(aka 'char *') and 'int')
if (tmp > 0)
    ~~~ ^ ~

JLib/Util/JTextFile.cpp:236:8: error: ordered comparison between pointer and zero ('int' and 's8 *'

(aka 'char *'))
  if (0 >= (end = strstr(ptr, "\"")))
      ~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~~

Reported by: antoine (via exp-run)