fix crash on startup caused by the hud_target_id panel

This class expects m_iTargetEntIndex to be zero-initalized, but they
didn't actually do that.

There are likely *tons* of other problems like this sitting around...

Author: ReplayCoding

src/game/client/tf/tf_hud_target_id.h

@@ -66,7 +66,7 @@ class CTargetID : public CHudElement, public vgui::EditablePanel
 	int				m_iLastEntIndex;
 	float			m_flLastChangeTime;
 	float			m_flTargetRetainFOV;
-	int				m_iTargetEntIndex;
+	int				m_iTargetEntIndex = 0; // Depends on being set to zero, but never set at construction!
 	bool			m_bLayoutOnUpdate;
 
 	vgui::Label				*m_pTargetNameLabel;