Fix missing Leave call button for guests in voice rooms

[Naved994]

Problem

Guests in voice rooms can join a call, but the "Leave call" button is hidden, leaving them without a clear way to leave the call through the UI.

Change

Updated the call button visibility logic so that:

• Guests who are not in a voice-room call do not see the call button.
• Guests who have already joined the call can see the "Leave call" button.
• Existing behavior for other users remains unchanged.

Implementation

Updated src/components/CallView/BottomBar.vue to use the current call state when deciding whether to display the CallButton.

Addresses #18844

[Antreesy]

It will be always shown now, because isInCall is always truthy.

Please read the issue before implementation,this change doesn't address raised questions