Fix wrong calculation of frames in bacapp_data_len (#491)

* Fixed wrong calculation of data length.  In cases when 2 sets of opening & closing tags (first opening tag context tag is 3, second is 0) were sent, one of the frames wasn't added, and the resulted sum was wrong

* Added unit test for case with two sets of opening & closing tags

src/bacnet/bacapp.c

@@ -1546,6 +1546,8 @@ int bacapp_data_len(
             } else if (tag_number == opening_tag_number) {
                 total_len_enable = true;
                 opening_tag_number_counter++;
+            } else {
+                total_len_enable = true;
             }
         } else if (bacnet_is_closing_tag(apdu, apdu_len_max)) {
             len = bacnet_tag_number_and_value_decode(

test/bacnet/bacapp/src/main.c

@@ -811,6 +811,23 @@ static void testBACnetApplicationDataLength(void)
     /* verify the length of the data inside the opening/closing tags */
     len = bacapp_data_len(&apdu[0], apdu_len, PROP_REQUESTED_SHED_LEVEL);
     zassert_equal(test_len, len, NULL);
+
+    /* 7. context opening & closing tag */
+    test_len = 0;
+    apdu_len = 0;
+    len = encode_opening_tag(&apdu[apdu_len], 3);
+    apdu_len += len;
+    len = encode_opening_tag(&apdu[apdu_len], 0);
+    apdu_len += len;
+    test_len += len;
+    len = encode_closing_tag(&apdu[apdu_len], 0);
+    apdu_len += len;
+    test_len += len;
+    len = encode_closing_tag(&apdu[apdu_len], 3);
+    apdu_len += len;
+    /* verify the length of the data inside the opening/closing tags */
+    len = bacapp_data_len(&apdu[0], apdu_len, PROP_WEEKLY_SCHEDULE);
+    zassert_equal(test_len, len, NULL);
 }
 
 /**