Fix Load File mech lookup: use stock_array to get chassis name

mech[j] in the flat sorted array hits variant entries (e.g. 'Assassin2 A'
sorts before 'AssassinII' alphabetically, pushing all subsequent chassis
indices off by 1 or more). The script's stock_array[] maps each chassis
index -> its actual position in the flat mech[] array, bypassing variant
entries.

Fix: mech[allowed_mechs[j]] -> mech[stock_array[allowed_mechs[j]]]

Only stock (chassis) names are supported in Mech= field. Operators can
adjust variants manually after Load File is clicked. No rebuild required
(script-only change).

Gameleap/mw4/Content/ShellScripts/ConLobby.script

@@ -1726,9 +1726,11 @@ main
                     if (!equal$(szAutoMech, ""))
                     {
 #if USE_ALLOWED_MECHS
+                        // stock_array[j] = index in mech[] where chassis j lives (skips variant entries).
+                        // mech[allowed_mechs[j]] would hit variant names; stock_array corrects this.
                         for (j = 0; j < MAX_ALLOWED_MECHS; j++)
                         {
-                            if equal$(mech[allowed_mechs[j]], szAutoMech)
+                            if equal$(mech[stock_array[allowed_mechs[j]]], szAutoMech)
                             {
                                 o_mech_variant[k].nselected = j
                                 break