Fix file upload with header merge

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/models/translation.py

@@ -1081,7 +1081,7 @@ class Translation(models.Model, URLMixin, PercentMixin, LoggerMixin):
                 # Optionally merge header
                 if unit2.unit.isheader():
                     if isinstance(store1, poheader.poheader):
-                        store1.mergeheaders(store2)
+                        store1.mergeheaders(store2.store)
                     continue
 
                 # Find unit by ID

weblate/trans/tests/test_files.py

@@ -86,6 +86,25 @@ class ImportTest(ImportBaseTest):
         unit = self.get_unit()
         self.assertEqual(unit.target, TRANSLATION_PO)
 
+    def test_import_header(self):
+        '''
+        Test importing with header merge.
+        '''
+        response = self.do_import(
+            merge_header='1',
+        )
+        self.assertRedirects(response, self.translation_url)
+
+        # Verify stats
+        translation = self.get_translation()
+        self.assertEqual(translation.translated, 1)
+        self.assertEqual(translation.fuzzy, 0)
+        self.assertEqual(translation.total, 4)
+
+        # Verify unit
+        unit = self.get_unit()
+        self.assertEqual(unit.target, TRANSLATION_PO)
+
     def test_import_author(self):
         '''
         Test importing normally.