mk: Don't run mkhelpers if mode is set

If the mode string is empty, then it's a build command.

See commit:

commit b1ea416575
Author: Leah Rowe <leah@libreboot.org>
Date:   Wed Apr 23 03:54:08 2025 +0100

    mk: remove mkhelp() and use x_() instead

This commit removed the following check:

If mode isn't set, run an mkhelper, otherwise don't.

Because this simplification removed that behaviour,
running e.g. "./mk -m coreboot x200_8mb" would result
in the mkcorebootbin function being executed, which is
normally putting the coreboot rom together.

Since it wasn't built in this case, an error is thrown.
This change therefore restores the previous behaviour,
fixing the bug.

First reported in this error report:
https://codeberg.org/libreboot/lbmk/issues/306

This commit fixes the issue.

Signed-off-by: Leah Rowe <leah@libreboot.org>

mk

@@ -191,7 +191,7 @@ build_targets()
 		printf "'make %s', '%s', '%s'\n" "$mode" "$project" "$target"
 		x_ handle_defconfig
 
-		x_ $postmake
+		[ -n "$mode" ] || x_ $postmake
 	done; :
 }
 
@@ -418,14 +418,14 @@ handle_makefile()
 
 run_make_command()
 {
-	x_ $premake
+	[ -n "$mode" ] || x_ $premake
 
 	$dry check_cmake "$srcdir" && [ -z "$mode" ] && \
 	    $dry check_autoconf "$srcdir"
 	$dry check_makefile "$srcdir" || return 1
 
 	$dry x_ make -C "$srcdir" $mode -j$XBMK_THREADS $makeargs
-	x_ $mkhelper
+	[ -n "$mode" ] || x_ $mkhelper
 
 	[ "$mode" != "clean" ] || \
 	    $dry make -C "$srcdir" $cleanargs distclean || :; :