telegram-chat: convert the message (command) to string

RouterOS 7.15beta4 fixed a bug in JSON parser:

*) console - do not convert string to array in ":deserialize" command;

Before that change commands with a comma caused very crazy issues. Let's
convert the message to a string. This does not give exactly the expected
result, but mitigates telegram-chat to explode.

A command like...

    /ip/address/print proplist=address,network;

... is converted to...

    /ip/address/print proplist=address;network;

... and results in:

    Columns: ADDRESS
    # ADDRESS
    0 10.0.0.1/24
    1 127.0.0.1/8
    bad command name network (line 1 column 36)

0 files changed, 0 insertions, 0 deletions