(get-membership-old): Fixed error in description of index-out-of-range.

(get-membership): Ditto.

doc/Protocol-A.texi

@@ -5186,7 +5186,7 @@ The person @rarg{person} does not exist.
 @item undefined-conference
 The conference @rarg{person} does not exist or is secret.
 @item index-out-of-range
-@rarg{first} is higher than the index of the first conference in the
+@rarg{first} is higher than the index of the last conference in the
 person's membership list.
 @end table
 
@@ -7286,7 +7286,7 @@ The person @rarg{person} does not exist.
 @item undefined-conference
 The conference @rarg{person} does not exist or is secret.
 @item index-out-of-range
-@rarg{first} is higher than the index of the first conference in the
+@rarg{first} is higher than the index of the last conference in the
 person's membership list.
 @end table