Make PramValues follow expectations

1. The keys are expected (not guaranteed) to be integers starting at 1. They previously started at 0.
2. The values should be undef if not yet bound

dbdimp.c

@@ -4026,9 +4026,17 @@ dbd_st_FETCH_internal(
             I32 keylen;
             for (n= 0; n < DBIc_NUM_PARAMS(imp_sth); n++)
             {
-                keylen= sprintf(key, "%d", n);
-                (void)hv_store(pvhv, key,
-                         keylen, newSVsv(imp_sth->params[n].value), 0);
+                // https://metacpan.org/pod/DBI#ParamValues says keys
+                // are typically integers starting at 1
+                // values should be undef if not yet bound
+                keylen= sprintf(key, "%d", n+1);
+                if (imp_sth->params[n].value) {
+                    (void)hv_store(pvhv, key,
+                             keylen, newSVsv(imp_sth->params[n].value), 0);
+                } else {
+                    (void)hv_store(pvhv, key,
+                             keylen, &PL_sv_undef, 0);
+                }
             }
         }
         retsv= sv_2mortal(newRV_noinc((SV*)pvhv));