Use xmalloc where appropriate.

src/varscan.c

@@ -1028,7 +1028,7 @@ void varDefTable(int varID, int tableID)
 void varDefEnsembleInfo(int varID, int ens_idx, int ens_count, int forecast_type)
 {
   if ( vartable[varID].ensdata == NULL )
-      vartable[varID].ensdata = (ensinfo_t *) malloc( sizeof( ensinfo_t ) );
+      vartable[varID].ensdata = (ensinfo_t *)xmalloc( sizeof( ensinfo_t ) );
 
   vartable[varID].ensdata->ens_index = ens_idx;
   vartable[varID].ensdata->ens_count = ens_count;