AK3: fix repack return check with magiskboot

META-INF/com/google/android/updater-script

@@ -3,4 +3,4 @@
 # Dummy file; update-binary is a shell script (DO NOT CHANGE)
 #
 #
-# AK_BASE_VERSION=20230822
+# AK_BASE_VERSION=20230828

tools/ak3-core.sh

@@ -386,12 +386,14 @@ flash_boot() {
       *) export PATCHVBMETAFLAG=false;;
     esac;
     $bin/magiskboot repack $nocompflag $bootimg $home/boot-new.img;
-    unset PATCHVBMETAFLAG;
   fi;
   if [ $? != 0 ]; then
     abort "Repacking image failed. Aborting...";
   fi;
-  [ -f .magisk ] && touch $home/magisk_patched;
+  if [ -f .magisk ]; then
+    touch $home/magisk_patched;
+    unset PATCHVBMETAFLAG;
+  fi;
 
   cd $home;
   if [ -f "$bin/futility" -a -d "$bin/chromeos" ]; then