Read the boot loader's config only where the migration needs it

The migration read ESP_PATH from /etc/default/limine at its top. On a
machine without that file sed fails, and under bash -euo pipefail the
migration stopped there with an error, before the check that lets a
machine without Limine skip it.

The read moves to after the rebuild, the one place the path is used; a
path given for the tests is taken first, and a missing file means /boot.

migrations/1791581004.sh

@@ -12,8 +12,6 @@ defaults_conf="${OMARCHY_LIMINE_DEFAULTS_CONF:-/etc/limine-entry-tool.d/omarchy-
 running_cmdline="${OMARCHY_RUNNING_CMDLINE:-/proc/cmdline}"
 rebuild_marker="${OMARCHY_LIMINE_REBUILD_MARKER:-/var/lib/omarchy/migrations/1791581004}"
 param="systemd.tty.term.console=dumb"
-esp=$(sed -n 's/^ESP_PATH=["'\'']\?\([^"'\'']*\).*/\1/p' /etc/default/limine 2>/dev/null | tail -n 1)
-limine_conf="${OMARCHY_LIMINE_CONF:-${esp:-/boot}/limine.conf}"
 
 omarchy-cmd-present limine-mkinitcpio || exit 0
 [[ -f $defaults_conf && -r $running_cmdline ]] || exit 0
@@ -31,6 +29,17 @@ grep -Eq "^KERNEL_CMDLINE\[default\]\+=\".*${param//./\\.}.*\"" "$defaults_conf"
 echo "The booted kernel is missing $param; rebuilding the boot image"
 sudo limine-mkinitcpio
 
+# The boot menu is on the ESP, which /etc/default/limine names; /boot when it
+# does not, or is not there.
+limine_conf="${OMARCHY_LIMINE_CONF:-}"
+if [[ -z $limine_conf ]]; then
+  esp=""
+  if [[ -r /etc/default/limine ]]; then
+    esp=$(sed -n 's/^ESP_PATH=["'\'']\?\([^"'\'']*\).*/\1/p' /etc/default/limine | tail -n 1)
+  fi
+  limine_conf="${esp:-/boot}/limine.conf"
+fi
+
 # limine-mkinitcpio carries on past a kernel it could not build, a full boot
 # partition for one, and still exits 0. Done means a boot entry has the
 # parameter: without that the migration stays pending and the next update