Fix s_server/s_client handling of the split_send_frag argument

Ensure that a value of 0 is correctly handled for the split_send_frag
argument.

Reviewed-by: Tim Hudson <tjh@openssl.org>
diff --git a/apps/s_client.c b/apps/s_client.c
index 5a5a90b..a1ef64b 100644
--- a/apps/s_client.c
+++ b/apps/s_client.c
@@ -1389,8 +1389,11 @@
         case OPT_SPLIT_SEND_FRAG:
             split_send_fragment = atoi(opt_arg());
             if (split_send_fragment == 0) {
-                /* Not allowed - set to a deliberately bad value */
-                split_send_fragment = -1;
+                /*
+                 * Not allowed - set to a deliberately bad value so we get an
+                 * error message below
+                 */
+                split_send_fragment = SSL3_RT_MAX_PLAIN_LENGTH + 1;
             }
             break;
         case OPT_MAX_PIPELINES: