graphviz: fix test errors on the mac.

extra/graphviz/ffi/ffi.factor

@@ -104,8 +104,11 @@ M: ffi-errors error.
     " error(s) occurred while rendering." print
     "(The messages were probably printed to STDERR.)" print ;
 
+: ?ffi-errors ( n -- )
+    [ ffi-errors ] unless-zero ; inline
+
 : gvFreeContext ( gvc -- )
-    int-gvFreeContext [ ffi-errors ] unless-zero ;
+    int-gvFreeContext ?ffi-errors ;
 
 DESTRUCTOR: gvFreeContext
 

extra/graphviz/render/render.factor

@@ -83,9 +83,8 @@ M: unsupported-engine summary
         graph id>> graph kind agopen &agclose :> g
         g graph build-alien
         g -K compute-engine :> engine
-        gvc g engine gvLayout drop
-        [ gvc g -T -o gvRenderFilename drop -o ]
-        [ gvc g gvFreeLayout drop ] [ ] cleanup
+        gvc g engine gvLayout ?ffi-errors
+        gvc g -T -o gvRenderFilename ?ffi-errors -o
     ] with-destructors ;
 
 : (preview) ( graph -- -o )