list: better options parsing

shellpki

@@ -215,7 +215,7 @@ Revoke a client cert with is commonName (CN) :
 
 List all actually valid commonName (CN) :
 
-    ${0} list [-a|v|r]
+    ${0} list [-a|--all|-v|--valid|-r|--revoked]
 
 Check expiration date of valid certificates :
 
@@ -763,6 +763,11 @@ list() {
         exit 0
     fi
 
+    if [ -z "${1}" ]; then
+        show_usage >&2
+        exit 1
+    fi
+
     list_valid=0
     list_revoked=1