Fix _adapter_statistics_as_json bug with one_line=True

Discovered and initial fix suggested by @y9c

Closes #803
Closes #804

Author: marcelm

src/cutadapt/report.py

@@ -272,7 +272,7 @@ def _adapter_statistics_as_json(
         adapter = adapter_statistics.adapter
         ends: List[Optional[Dict[str, Any]]] = []
         total_trimmed_reads = 0
-        make_line = OneLine if one_line else list
+        make_line = OneLine if one_line else lambda value: value
         for end_statistics in adapter_statistics.end_statistics():
             if end_statistics is None:
                 ends.append(None)