listener: don't crash if pprint fails.

basis/listener/listener.factor

@@ -93,6 +93,13 @@ t error-summary? set-global
         ] tabular-output nl
     ] unless-empty ;
 
+: print-stack ( seq -- )
+    [
+        [ short. ]
+        [ drop "~pprint error~" swap write-object nl ]
+        recover
+    ] each ;
+
 : trimmed-stack. ( seq -- )
     dup length max-stack-items get > [
         max-stack-items get cut*
@@ -100,7 +107,7 @@ t error-summary? set-global
             [ length number>string "(" " more items)" surround ] keep
             write-object nl
         ] dip
-    ] when stack. ;
+    ] when print-stack ;
 
 : datastack. ( datastack -- )
     display-stacks? get [