[core] Actually require Magisk v21+ (#458)

* Because magisk --path is not available till this version.

core/template_override/customize.sh

@@ -51,6 +51,7 @@ extract "$ZIPFILE" 'util_functions.sh' "${TMPDIR}"
 . ${TMPDIR}/util_functions.sh
 
 check_android_version
+check_magisk_version
 
 extract "$ZIPFILE" 'riru.sh' "$TMPDIR"
 . $TMPDIR/riru.sh

core/template_override/util_functions.sh

@@ -20,6 +20,11 @@
 
 check_magisk_version() {
   ui_print "- Magisk version: ${MAGISK_VER_CODE}"
+  if [ "$MAGISK_VER_CODE" -lt 21000 ]; then
+      ui_print "${POUNDS}"
+      ui_print "Please install Magisk v21+!"
+      abortC "${POUNDS}"
+  fi
 }
 
 require_new_android() {