Adjust guard mode patch to ignore AI-owned aircraft

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

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