AK3: fix unset PATCHVBMETAFLAG, only read kernel strings once

tools/ak3-core.sh

@@ -355,12 +355,14 @@ flash_boot() {
             echo "Attempting kernel unpack with busybox $comp..." >&2;
             $comp -dc $kernel > kernel;
           fi;
-          if strings kernel 2>/dev/null | grep -q -E '^/data/adb/ksud$'; then
+          strings kernel > stringstmp 2>/dev/null;
+          if grep -q -E '^/data/adb/ksud$' stringstmp; then
             touch $home/kernelsu_patched;
-            strings kernel 2>/dev/null | grep -E -m1 'Linux version.*#' > $home/vertmp;
+            grep -E -m1 'Linux version.*#' stringstmp > $home/vertmp;
           else
             ui_print " " "Warning: No KernelSU support detected in kernel!";
           fi;
+          rm -f stringstmp;
           if [ "$comp" ]; then
             $bin/magiskboot compress=$comp kernel kernel.$comp;
             if [ $? != 0 ] && $comp --help 2>/dev/null; then
@@ -390,10 +392,8 @@ flash_boot() {
   if [ $? != 0 ]; then
     abort "Repacking image failed. Aborting...";
   fi;
-  if [ -f .magisk ]; then
-    touch $home/magisk_patched;
-    unset PATCHVBMETAFLAG;
-  fi;
+  [ "$PATCHVBMETAFLAG" ] && unset PATCHVBMETAFLAG;
+  [ -f .magisk ] && touch $home/magisk_patched;
 
   cd $home;
   if [ -f "$bin/futility" -a -d "$bin/chromeos" ]; then