Revert "Removed unused grid_t member extraData."

* extraData will be used after all.

src/cdf_lazy_grid.c

@@ -29,6 +29,7 @@ static bool cdfLazyInitialized;
 void
 cdfLazyGridDestroy(struct cdfLazyGrid *lazyGrid)
 {
+  lazyGrid->base.extraData = NULL;
   if (lazyGrid->base.area == cdfPendingLoad) lazyGrid->base.area = NULL;
   if (lazyGrid->base.x.vals == cdfPendingLoad) lazyGrid->base.x.vals = NULL;
   if (lazyGrid->base.y.vals == cdfPendingLoad) lazyGrid->base.y.vals = NULL;

src/grid.c

@@ -162,6 +162,8 @@ grid_init(grid_t *gridptr)
   gridptr->atts.nelems = 0;
 
   cdiDefVarKeyInt(&gridptr->keys, CDI_KEY_DATATYPE, CDI_DATATYPE_FLT64);
+
+  gridptr->extraData = NULL;
 }
 
 static void

src/grid.h

@@ -132,6 +132,7 @@ struct grid_t
   const struct gridVirtTable *vtable;
   cdi_keys_t keys;
   cdi_atts_t atts;
+  void *extraData;
 };
 
 void grid_init(grid_t *gridptr);