inject.sh: simplify. and remove unnecessary check

checking whether archivename is empty isn't needed, because
the case/switch afterward would catch this condition.

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

include/inject.sh

@@ -38,7 +38,7 @@ inject()
 	esac
 	[ "$new_mac" = "keep" ] && new_mac=""
 
-	check_release
+	x_ e "$archive" f && check_release
 	check_target && patch_release
 
 	[ "$xchanged" = "y" ] && remktar
@@ -52,10 +52,8 @@ inject()
 check_release()
 {
 	[ -L "$archive" ] && err "'$archive' is a symlink"
-	e "$archive" f missing && err "'$archive' missing"
 
 	archivename="`basename "$archive"`" || err "Can't get '$archive' name"
-	[ -z "$archivename" ] && err "Can't determine archive name"
 
 	case "$archivename" in
 	*_src.tar.xz) err "'$archive' is a src archive, silly!" ;;