Fix a special case in message history retrieval.

This function is not yet completely tested, 

coreapi/message_storage.c

@@ -371,7 +371,7 @@ MSList *linphone_chat_room_get_history_range(LinphoneChatRoom *cr, int startm, i
 
 	if (startm<0) startm=0;
 
-	if (endm>0&&endm>=startm){
+	if ((endm>0&&endm>=startm) || (startm == 0 && endm == 0) ){
 		buf2=ms_strdup_printf("%s LIMIT %i ",buf,endm+1-startm);
 		ms_free(buf);
 		buf = buf2;

tester/message_tester.c

@@ -1045,6 +1045,10 @@ static void history_messages_count() {
 		CU_ASSERT_EQUAL(ms_list_size(messages), 10);
 		ms_list_free_with_data(messages, (void (*)(void*))linphone_chat_message_unref);
 
+		messages=linphone_chat_room_get_history(chatroom,1);
+		CU_ASSERT_EQUAL(ms_list_size(messages), 1);
+		ms_list_free_with_data(messages, (void (*)(void*))linphone_chat_message_unref);
+
 		messages=linphone_chat_room_get_history(chatroom,0);
 		CU_ASSERT_EQUAL(linphone_chat_room_get_history_size(chatroom), 1270);
 		CU_ASSERT_EQUAL(ms_list_size(messages), 1270);