spgist rangetypes compiler warning (gcc 7.2.0)

Hi,

while compiling on gcc 7.2.0 (on ARM), I got this warning:

    rangetypes_spgist.c: In function 'spg_range_quad_inner_consistent':
    rangetypes_spgist.c:559:29: warning: comparison between pointer and
    zero character constant [-Wpointer-compare]
          if (in->traversalValue != (Datum) 0)
                                 ^~
    rangetypes_spgist.c:559:10: note: did you mean to dereference the
    pointer?
          if (in->traversalValue != (Datum) 0)
              ^

I believe we should simply treat the traversalValue as pointer, and
change the condition to

    if (in->traversalValue)

Patch attached.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
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