goto: add null checking about the return value of elm_entry_entry_get

Summary:
there is no null checking condition,
so I added the null checking condition about the return value of elm_entry_entry_get.
@fix

Reviewers: Jaehyun_Cho, NikaWhite, Hermet

Reviewed By: Hermet

Differential Revision: https://phab.enlightenment.org/D3763

src/bin/goto.c

@@ -78,6 +78,9 @@ entry_changed_cb(void *data, Evas_Object *obj, void* event_info EINA_UNUSED)
 {
    goto_data *gd = data;
    const char *txt = elm_entry_entry_get(obj);
+
+   if (!txt) return;
+
    if (txt[0] == 0) return;
 
    int line = atoi(txt);