LP:882489 - Valgrind warning with progress reporting

When executing SHOW PROCESSLIST concurrently with SELECT queries, valgrind reports the following:

==3857== Conditional jump or move depends on uninitialised value(s)
==3857== at 0x6D2916: __printf_fp (in /lib/libc-2.12.1.so)
==3857== by 0x6CD4F9: vfprintf (in /lib/libc-2.12.1.so)
==3857== by 0x6F4C1F: vsnprintf (in /lib/libc-2.12.1.so)
==3857== by 0x6D6C21: snprintf (in /lib/libc-2.12.1.so)
==3857== by 0x82936D3: String::set_real(double, unsigned int, charset_info_st const*) (sql_string.cc:194)
==3857== by 0x828EE44: Protocol_text::store(double, unsigned int, String*) (protocol.cc:1062)
==3857== by 0x842F86D: mysqld_list_processes(THD*, char const*, bool) (sql_show.cc:2022)
==3857== by 0x82AF600: mysql_execute_command(THD*) (sql_parse.cc:3422)
==3857== by 0x82B74E2: mysql_parse(THD*, char*, unsigned int, char const**) (sql_parse.cc:6112)
==3857== by 0x82A98BF: dispatch_command(enum_server_command, THD*, char*, unsigned int) (sql_parse.cc:1221)
==3857== by 0x82A8D1A: do_command(THD*) (sql_parse.cc:916)
==3857== by 0x82A5CFE: handle_one_connection (sql_connect.cc:1191)
==3857== by 0x821918: start_thread (in /lib/libpthread-2.12.1.so)
==3857== by 0x76ACCD: clone (in /lib/libc-2.12.1.so)

line 2022 in sql_show.cc is

protocol->store(thd_info->progress, 3, &store_buffer);

let me know if a test case or a core file is required.