clang: suppress a warning

Initialize variable explicitly.

    ii.c:2909:17: warning: variable 'dcn' is used uninitialized whenever '||'
          condition is true [-Wsometimes-uninitialized]
                if (!actual_chunk_size || !(rc = chunk_new(ctx, ii, &dcn,...
                    ^~~~~~~~~~~~~~~~~~
    ii.c:2911:50: note: uninitialized use occurs here
                  fake_map2(ctx, ii->chunk, &dw, dc, dcn, actual_chunk_size);
                                                     ^~~
    ii.c:2909:17: note: remove the '||' if its condition is always false
                if (!actual_chunk_size || !(rc = chunk_new(ctx, ii, &dcn,...
                    ^~~~~~~~~~~~~~~~~~~~~
    ii.c:2886:30: note: initialize the variable 'dcn' to silence this warning
      uint32_t ds, pseg, scn, dcn;
                                 ^
                                  = 0

lib/ii.c

@@ -2883,7 +2883,7 @@ buffer_flush(grn_ctx *ctx, grn_ii *ii, uint32_t seg, grn_hash *h)
   grn_io_win sw, dw;
   buffer *sb, *db = NULL;
   uint8_t *dc, *sc = NULL;
-  uint32_t ds, pseg, scn, dcn;
+  uint32_t ds, pseg, scn, dcn = 0;
   if (ii->header->binfo[seg] == NOT_ASSIGNED) { return GRN_FILE_CORRUPT; }
   if ((ds = segment_get(ctx, ii)) == MAX_PSEG) { return GRN_NO_MEMORY_AVAILABLE; }
   pseg = buffer_open(ctx, ii, SEG2POS(seg, 0), NULL, &sb);