Fix ht default size test

in the line:

  size != 0 ? : (size = DEFAULT_HT_SIZE);

we should notice that the lack of ( ) around "size != 0" leads to the
following behavior: the compiler will try to evaluate

  "0 ? : (size = DEFAULT_HT_SIZE)"

and compare it to size, which is not the expected behavior.

Use a standard "if (cond)" test instead. The ? : expression is not
needed here anyway, it just complicates the code.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>