obs-browser: Ensure saved source is alive

[walker-WSH]

Description

In browser-client, created source is saved into two lists:

std::vector<obs_source_t*> audio_sources;
std::unordered_map<int, AudioStream> audio_streams;

But there is no reference for audio_sources.
I meet a crash as below:

Motivation and Context

How Has This Been Tested?

Types of changes

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[gxalpha]

Is there any particular reason why you're still running a CEF older than 4103?
I'm asking since we're looking to update our CEF again for the next version of OBS, in which case this code would get removed (we're usually supporting the current plus the last CEF).

[walker-WSH]

Is there any particular reason why you're still running a CEF older than 4103? I'm asking since we're looking to update our CEF again for the next version of OBS, in which case this code would get removed (we're usually supporting the current plus the last CEF).

since the crash in #360 ， I am still using the old CEF.

that crash of obs-browser-page.exe can be reproduced easy on my PC