[3.x] Change `msg.html_text` behaviour

[Olegt0rr]

Description

Every time when I use message.html_text in my projects, I use construct like this:

text = message.html_text if (message.text or message.caption) else None

cause with current behavior, calling html_text on None will raise an error TypeError: This message doesn't have any text.

With try I also should use code like this:

try:
    text = message.html_text
except TypeError:
    text = None

Describe the solution you'd like

I'd like to make it return None instead of raising an error.
This way it will be more similar to basic message and caption params behaviour. If it's empty - return None.