Updating logic so that edge iterator does not erase the contents of the queue during next call

Summary: The edge iterator wipes out the previous contents of the queue while iterating through the response

Test Plan:
The test runs are below:
ritu-mbp:python-ads-sdk ritu$ python -i facebookads/bootstrap.py
  >>> act = AdAccount('act_219066941615718')
  >>> adsets = act.get_ad_sets()
  >>> adsets
  [<AdSet> {
      "id": "6034561139616"
  }, <AdSet> {
      "id": "6033251546616"
  }, <AdSet> {
      "id": "6031938715216"
  }, <AdSet> {
      "id": "6031544286616"
  }]

  >>> for adset in adsets:
  ...     print(adset)
  ...
  <AdSet> {
      "id": "6034561139616"
  }
  <AdSet> {
      "id": "6033251546616"
  }
  <AdSet> {
      "id": "6031938715216"
  }
  >>> adsets
  [<AdSet> {
      "id": "6034561139616"
  }, <AdSet> {
      "id": "6033251546616"
  }, <AdSet> {
      "id": "6031938715216"
  }, <AdSet> {
      "id": "6031544286616"
  }]
  >>> exit()

Unit Test and Integration test run:

ritu-mbp:python-ads-sdk ritu$ python -m facebookads.test.unit
............................
----------------------------------------------------------------------
Ran 28 tests in 0.015s

OK
ritu-mbp:python-ads-sdk ritu$ python -m facebookads.test.integration
....................
----------------------------------------------------------------------
Ran 20 tests in 34.884s

OK
ritu-mbp:python-ads-sdk ritu$ python3 -m facebookads.test.integration
....................
----------------------------------------------------------------------
Ran 20 tests in 24.358s

OK
ritu-mbp:python-ads-sdk ritu$ python3 -m facebookads.test.unit
............................
----------------------------------------------------------------------
Ran 28 tests in 0.017s

OK

Author: Rituparna Mukherjee

facebookads/objects.py

@@ -119,6 +119,7 @@ def __init__(
             target_objects_class.get_endpoint(),
         )
         self._queue = []
+        self._count = 0
         self._finished_iteration = False
         self._total_count = None
         self._include_summary = include_summary
@@ -133,12 +134,14 @@ def __iter__(self):
         return self
 
     def __next__(self):
+        self._count += 1
         # Load next page at end.
+        # If the queue counter equals the length of the queue and
         # If load_next_page returns False, raise StopIteration exception
-        if not self._queue and not self.load_next_page():
+        if (self._count == len(self._queue) and not self.load_next_page()):
             raise StopIteration()
 
-        return self._queue.pop(0)
+        return self._queue[self._count-1]
 
     # Python 2 compatibility.
     next = __next__
@@ -187,6 +190,8 @@ def load_next_page(self):
             self._total_count = response['summary']['total_count']
 
         self._queue = self.build_objects_from_response(response)
+        self._count = 0
+
         return len(self._queue) > 0
 
     def build_objects_from_response(self, response):