Fixed that caused failure in --ps binlog_encryption.rpl_gtid_basic

Problem was that replace_dynstr_append_mem() assumed strings are
null terminated which is not always the case.

client/mysqltest.cc

@@ -11145,13 +11145,16 @@ void replace_dynstr_append_mem(DYNAMIC_STRING *ds, const char *val, size_t len)
     {
       /* Convert to lower case, and do this first */
       char *c= lower;
-      for (const char *v= val;  *v;  v++)
+      for (const char *v= val, *end_v= v + len;  v < end_v;  v++)
         *c++= my_tolower(charset_info, *v);
       *c= '\0';
       /* Copy from this buffer instead */
     }
     else
-      memcpy(lower, val, len+1);
+    {
+      memcpy(lower, val, len);
+      lower[len]= 0;
+    }
     fix_win_paths(lower, len);
     val= lower;
   }

sql/sql_class.cc

@@ -3002,7 +3002,8 @@ int select_send::send_data(List<Item> &items)
 
   thd->inc_sent_row_count(1);
 
-  if (thd->vio_ok())
+  /* Don't return error if disconnected, only if write fails */
+  if (likely(thd->vio_ok()))
     DBUG_RETURN(protocol->write());
 
   DBUG_RETURN(0);