[TF2 SDK] Extra footstep sounds play when walking after first spawn

[Tkain]

On a freshly built copy of the TF2 SDK, after a player spawns into a map for the first time, more footstep sounds than usual will play when the player moves around. This can be seen in the following video:

footstep-bug.mp4

I was able to reproduce this bug fairly consistently by simply starting a new server and then choosing a team and class. Notably, the extra footstep sounds seem to go away after the "waiting for players" timer expires (and the player is reset).

In my testing, I've found that these extra footstep sounds are playing because of animation events triggered by the player entity on the client side. Normally, these animation events shouldn't be triggered because the client player is not marked as visible, which causes C_BaseAnimating::DoAnimationEvents to return before running animation events:

source-sdk-2013/src/game/client/c_baseanimating.cpp

Lines 3568 to 3572 in 0759e2e

	// If we're invisible, don't draw the muzzle flash
	bool bIsInvisible = !IsVisible() && !IsViewModel() && !IsMenuModel();
	if ( bIsInvisible && !clienttools->IsInRecordingMode() )
	return;

However, after spawning for the first time, IsVisible() seems to return true, causing animation events like the footstep event to play anyway. Once the "waiting for players" timer expires and the player is respawned, IsVisible() seemingly returns false as normal.

I haven't tested mainline TF2 for this bug as thoroughly as the SDK, but I can't seem to reproduce this bug there.