Adjust guard mode patch to ignore AI-owned aircraft

Some Tiberian Sun singleplayer missions rely on the original behaviour with AI aircraft

Author: Rampastring

src/guard_mode_patch.asm

@@ -4,4 +4,30 @@
 
 ;;; http://www.ppmforums.com/viewtopic.php?t=38895
 ; # Units in Guard mode will no longer chase after enemies that move out of firing range
-@CLEAR 0x004A1AA8, 0x90, 0x004A1AAA
+; @CLEAR 0x004A1AA8, 0x90, 0x004A1AAA
+
+; Hack FootClass::Mission_Guard
+; Follow current target only if we are an AI-controlled aircraft.
+; Author: Rampastring
+hack 0x004A1AA0
+ ; Restore original code. Follow target if we are an engineer
+ test al, al
+ jnz 0x004A1AD6 ; continue with current target
+
+ mov ecx, esi ; this
+ mov eax, [esi] ; vtable
+ call [eax+2Ch] ; ObjectClass::What_Am_I()
+ cmp eax, 2 ; RTTI_AIRCRAFT
+ jne 0x004A1AAE ; if not aircraft: seek new target, idle if not found
+
+ mov ecx, [esi+0ECh] ; Owner
+ call 0x004CB990 ; HouseClass::Is_Human_Control()
+ test al, al
+ jnz 0x004A1AAE ; if human-controlled: seek new target, idle if not found
+
+ ; if we get here we know that 1) the foot object is an aircraft and 2) the aircraft is AI-controlled
+ ; check for its TarCom
+ mov ecx, [esi+11Ch] ; TechnoClass.TarCom
+ test ecx, ecx
+ jnz 0x004A1AD6 ; continue with current target
+ jmp 0x004A1AAE ; our tarcom is null, seek new target and idle if one is not found