env: Avoid clobbering an edited variable on ctrl-c

If readline says there was an error, don't write to the variable!

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>

common/cmd_nvedit.c

@@ -552,7 +552,8 @@ static int do_env_edit(cmd_tbl_t *cmdtp, int flag, int argc,
 	else
 		buffer[0] = '\0';
 
-	readline_into_buffer("edit: ", buffer, 0);
+	if (readline_into_buffer("edit: ", buffer, 0) < 0)
+		return 1;
 
 	return setenv(argv[1], buffer);
 }