Fix a couple bugs in unix.users and add unit tests

basis/unix/users/users-docs.factor

@@ -50,7 +50,7 @@ HELP: set-real-user
 HELP: user-passwd
 { $values
      { "obj" object }
-     { "passwd" passwd } }
+     { "passwd/f" "passwd or f" } }
 { $description "Returns the passwd tuple given a username string or user id." } ;
 
 HELP: username

basis/unix/users/users-tests.factor

@@ -24,3 +24,7 @@ IN: unix.users.tests
 [ ] [ effective-user-id [ ] with-effective-user ] unit-test
 
 [ ] [ [ ] with-user-cache ] unit-test
+
+[ "9999999999999999999" ] [ 9999999999999999999 username ] unit-test
+
+[ f ] [ 89898989898989898989898989898 user-passwd ] unit-test

basis/unix/users/users.factor

@@ -47,17 +47,18 @@ SYMBOL: user-cache
 : with-user-cache ( quot -- )
     [ <user-cache> user-cache ] dip with-variable ; inline
 
-GENERIC: user-passwd ( obj -- passwd )
+GENERIC: user-passwd ( obj -- passwd/f )
 
 M: integer user-passwd ( id -- passwd/f )
     user-cache get
-    [ at ] [ getpwuid passwd>new-passwd ] if* ;
+    [ at ] [ getpwuid [ passwd>new-passwd ] [ f ] if* ] if* ;
 
 M: string user-passwd ( string -- passwd/f )
     getpwnam dup [ passwd>new-passwd ] when ;
 
 : username ( id -- string )
-    user-passwd username>> ;
+    dup user-passwd
+    [ nip username>> ] [ number>string ] if* ;
 
 : user-id ( string -- id )
     user-passwd uid>> ;