Fix issue with atomic_compare_exchange_strong due to inappropriate type on 32 bit platforms

Signed-off-by: Christopher Schwartz <christopherschwartz@xrite.com>

Author: ChristopherSchwartzXRITE

src/lib/OpenEXRCore/chunk.c

@@ -565,7 +565,7 @@ extract_chunk_table (
     if (ctable == NULL)
     {
         int64_t      nread = 0;
-        uintptr_t    eptr = 0, nptr = 0;
+        uint64_t     eptr = 0, nptr = 0;
         int          complete = 1;
         uint64_t     maxoff   = ((uint64_t) -1);
         exr_result_t rv;