Fix race condition in CompareDataFrameStage (#935)

* Fixes intermittent segfault in `CompareDataFrameStage` and `ValidationStage`

Authors:
  - David Gardner (https://github.com/dagardner-nv)

Approvers:
  - Devin Robison (https://github.com/drobison00)
  - Christopher Harris (https://github.com/cwharris)

URL: #935

morpheus/stages/output/compare_dataframe_stage.py

@@ -107,13 +107,15 @@ def get_results(self, clear=True) -> dict:
         if self._reset_index:
             combined_df.reset_index(inplace=True)
 
+        results = compare_df.compare_df(self._compare_df,
+                                        combined_df,
+                                        include_columns=self._include_columns,
+                                        exclude_columns=self._exclude_columns,
+                                        replace_idx=self._index_col,
+                                        abs_tol=self._abs_tol,
+                                        rel_tol=self._rel_tol)
+
         if clear:
             self.clear()
 
-        return compare_df.compare_df(self._compare_df,
-                                     combined_df,
-                                     include_columns=self._include_columns,
-                                     exclude_columns=self._exclude_columns,
-                                     replace_idx=self._index_col,
-                                     abs_tol=self._abs_tol,
-                                     rel_tol=self._rel_tol)
+        return results