tree.sh: fix up copy_elf(), bad for loop

Because of how sh works, having just the [] line causes
sh to exit, annoyingly without an error message, but it
does cause a non-zero exit.

This bug will have already been triggering, before I added
the recent error handling on files for this for loop.

also do it to the other loop in lib.sh

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

include/lib.sh

@@ -111,7 +111,7 @@ fx_()
 dx_()
 {
 	[ ! -f "$2" ] || while read -r fx; do
-		$1 "$fx" || return 1
+		$1 "$fx" || return 1; :
 	done < "$2" || err "dx_ $*: cannot read '$2'"; :
 }