wrap.strings: empty strings should wrap as the indent.

basis/wrap/strings/strings-tests.factor

@@ -47,3 +47,5 @@ word wrap."""
 
 [ "" ] [ "" 10 wrap-string ] unit-test
 [ "Hello" ] [ "\nHello\n" 10 wrap-string ] unit-test
+
+{ " > > > " } [ "" 70 " > > > " wrap-indented-string ] unit-test

basis/wrap/strings/strings.factor

@@ -34,4 +34,4 @@ PRIVATE>
 
 : wrap-indented-string ( string width indent -- newstring )
     make-indent [ length - wrap-lines ] keep
-    '[ _ prepend ] map! join-lines ;
+    over empty? [ nip ] [ '[ _ prepend ] map! join-lines ] if ;