dc_get_chat_contacts should always return an array and never a null

pointer otherwise we break the ffi interface

src/dc_chat.rs

@@ -1410,10 +1410,9 @@ pub fn dc_get_chat_contacts(context: &Context, chat_id: u32) -> *mut dc_array_t
     /* Normal chats do not include SELF.  Group chats do (as it may happen that one is deleted from a
     groupchat but the chats stays visible, moreover, this makes displaying lists easier) */
 
-    if chat_id == 1 {
-        return std::ptr::null_mut();
-    }
 
+
+    let ret = if chat_id != 1 {
         // we could also create a list for all contacts in the deaddrop by searching contacts belonging to chats with
         // chats.blocked=2, however, currently this is not needed
 
@@ -1434,8 +1433,18 @@ pub fn dc_get_chat_contacts(context: &Context, chat_id: u32) -> *mut dc_array_t
 
                     Ok(ret.into_raw())
                 },
-        )
+            ).ok()
-        .unwrap_or_else(|_| std::ptr::null_mut())
+    } else {
+        None
+    };
+
+
+    if let Some(chat_contacts) = ret {
+        chat_contacts
+    } else {
+        dc_array_t::new(0).into_raw()
+    }
+
 }
 
 pub unsafe fn dc_get_chat(context: &Context, chat_id: uint32_t) -> *mut Chat {