bc: do not allocate line editing state until needed

function                                             old     new   delta
xc_read_line                                         324     353     +29
free_line_input_t                                     34      39      +5
xc_vm_init                                           656     640     -16
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 34/-16)             Total: 18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush.c b/shell/hush.c
index a8f7237..f0f0da7 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -2056,8 +2056,7 @@
 static void hush_exit(int exitcode)
 {
 #if ENABLE_FEATURE_EDITING_SAVE_ON_EXIT
-	if (G.line_input_state)
-		save_history(G.line_input_state);
+	save_history(G.line_input_state); /* may be NULL */
 #endif
 
 	fflush_all();