get_array_info() can modifiy DBADDR::pfield

Allow the record support function get_array_info()
to modify its first argument to provide a different
pointer from which values should be read.

Remember the original and restore it afterwards.

src/std/filters/arr.c

@@ -104,7 +104,9 @@ static db_field_log* filter(void* pvt, dbChannel *chan, db_field_log *pfl) {
         if (chan->addr.special == SPC_DBADDR &&
             nSource > 1 &&
             (prset = dbGetRset(&chan->addr)) &&
-            prset->get_array_info) {
+            prset->get_array_info)
+        {
+            void *pfieldsave = chan->addr.pfield;
             prec = dbChannelRecord(chan);
             dbScanLock(prec);
             prset->get_array_info(&chan->addr, &nSource, &offset);
@@ -126,6 +128,7 @@ static db_field_log* filter(void* pvt, dbChannel *chan, db_field_log *pfl) {
                 pfl->u.r.field = pdst;
             }
             dbScanUnlock(prec);
+            chan->addr.pfield = pfieldsave;
         }
 
     /* Extract from buffer */