fix(esx_lib/points): start the points loop only once

startLoop is called from the esx:playerLoaded handler in es_extended, which fires
again on every character switch, and the loop it creates runs `while true` with no
exit. Each relog therefore leaves another points thread running: they all scan the
same table, fire the same enter and leave callbacks, and none of them ever stop.

A guard makes a second call a no-op. The loop is meant to live for the resource
lifetime, so starting it twice is never right.

Measured in game on artifact 25770, counting scans over four seconds:
  before: 1.0 -> 2.0 -> 3.0 loops across two relogs
  after:  1.0 -> 1.0 -> 1.0
Points keep working, the surviving loop is unaffected.

Note this touches the same file as #1831, which guards the callbacks inside the
loop. The two changes are in different places and independent of each other.

[core]/esx_lib/imports/points/client.lua

@@ -4,6 +4,7 @@ xLib.points = {}
 local points = {}
 local insidePoints = {}
 local handleCount = 0
+local loopStarted = false
 
 ---@param coords vector3
 ---@param distance number
@@ -44,6 +45,12 @@ function xLib.points.hide(handle, hidden)
 end
 
 function xLib.points.startLoop()
+    if loopStarted then
+        return
+    end
+
+    loopStarted = true
+
     CreateThread(function()
         local lastScan = 0