i-t: don't try to import from empty cache

Chases 7c64ee9
 ("zfs-import-{cache,scan}: change condition to FileNotEmpty")

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#12108

contrib/initramfs/scripts/zfs

@@ -709,7 +709,8 @@ mountroot()
 
 	# ------------
 	# Look for the cache file (if any).
-	[ ! -f "${ZPOOL_CACHE}" ] && unset ZPOOL_CACHE
+	[ -f "${ZPOOL_CACHE}" ] || unset ZPOOL_CACHE
+	[ -s "${ZPOOL_CACHE}" ] || unset ZPOOL_CACHE
 
 	# ------------
 	# Compatibility: 'ROOT' is for Debian GNU/Linux (etc),