trees: fix build issue caused by bad elf check

we're not checking for bad elfs, but the check itself was bad

due to a quirk in how sh works. really, really obscure bug.

fixed now!

if the given directory didn't actually exist, or there were no
files in it, it'd be searching for the file named "*"

which is obviously wrong

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

script/trees

@@ -204,6 +204,7 @@ elfcheck()
 {
 	# TODO: very hacky check. do it properly (based on build.list)
 	for elftest in "$dest_dir"/*; do
+		[ -e "$elftest" ] || continue
 		e "$elftest" f && return 1
 	done
 }