ui.tools.listener: fix stream-read-unsafe

It was returning the number of requested bytes even if eof was encountered.

basis/ui/tools/listener/listener.factor

@@ -152,8 +152,9 @@ M: interactor stream-readln
 
 M:: interactor stream-read-unsafe ( n buf interactor -- count )
     n [ 0 ] [
+        drop
         interactor interactor-read dup [ "\n" join ] when
-        n short head-slice 0 buf copy
+        n short [ head-slice 0 buf copy ] keep
     ] if-zero ;
 
 M: interactor stream-read-partial-unsafe