CHUI-188 FIX for crash in adding chat participants. Modified the duplicated participants check procedure LLIMFloater::canAddSelectedToChat() to use the list, updated by LLSpeakerMgr instead of LLIMSession::mInitialTargetIDs list, which is initialized at session start and not updated afterwards.
CHUI-188 FIX for crash in adding chat participants.
Modified the duplicated participants check procedure LLIMFloater::canAddSelectedToChat() to use the list, updated by LLSpeakerMgr instead of LLIMSession::mInitialTargetIDs list, which is initialized at session start and not updated afterwards.

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