Try resetting previous_collection_start_nano

Fixes open-telemetry#3974

Author: ocelotl

opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/aggregation.py

@@ -764,16 +764,16 @@ def collect(
                     is AggregationTemporality.DELTA
                 ):
 
-                    if value_positive is None and value_negative is None:
-                        return None
-
                     previous_collection_start_nano = (
                         self._previous_collection_start_nano
                     )
                     self._previous_collection_start_nano = (
                         collection_start_nano
                     )
 
+                    if value_positive is None and value_negative is None:
+                        return None
+
                     return ExponentialHistogramDataPoint(
                         attributes=self._attributes,
                         start_time_unix_nano=previous_collection_start_nano,