Keep tlsrpt-collectd running when it receives a datagram it cannot use.

dump_path_for_invalid_datagram defaults to "", and Path("") is ".", so
the first datagram that is not UTF-8 or not JSON raises
IsADirectoryError inside the error handler and the daemon exits (8).
Anything that can write to the socket can stop the collector with one
byte. Save the datagram only when a dump path is set, and log instead
of dying when saving it fails. A JSON number or null (1, null) raised
TypeError in add_datagram and took the daemon down the same way; log
and drop it like the KeyError case.

--- a/tlsrpt_reporter/tlsrpt.py
+++ b/tlsrpt_reporter/tlsrpt.py
@@ -1693,6 +1693,20 @@
     except OSError as err:
         logger.error("Failed to remove existing socket %s during %s: %s", server_address, when, err)
 
+def dump_invalid_datagram(path, data):
+    """
+    Save an invalid datagram for debugging, if dump_path_for_invalid_datagram is configured.
+    Failing to save it must not stop the daemon.
+    :param path: the configured dump file name, empty to not save anything
+    :param data: the datagram as received
+    """
+    if path is None or path == "":
+        return
+    try:
+        Path(path).write_bytes(data)
+    except OSError as err:
+        logger.error("Could not save invalid datagram to %s: %s", path, err)
+
 def tlsrpt_collectd_daemon(config: ConfigCollectd):
     """
     Daemon function for collectd to be run after configuration was setup
@@ -1801,6 +1815,9 @@
                             collectd.add_datagram(j)
                         except KeyError as err:
                             logger.error("KeyError %s during processing datagram: %s", str(err), json.dumps(j))
+                        except TypeError as err:
+                            logger.error("TypeError %s during processing datagram: %s", str(err),
+                                         json.dumps(j))
             if had_data == 0:
                 for collectd in collectds:
                     collectd.socket_timeout()
@@ -1812,10 +1829,10 @@
             raise
         except UnicodeDecodeError as err:
             logger.error("Malformed utf8 data received: %s", str(err))
-            Path(config.dump_path_for_invalid_datagram).write_bytes(alldata)
+            dump_invalid_datagram(config.dump_path_for_invalid_datagram, alldata)
         except json.decoder.JSONDecodeError as err:
             logger.error("JSON decode error: %s", str(err))
-            Path(config.dump_path_for_invalid_datagram).write_text(alldata.decode("utf-8"), encoding="utf-8")
+            dump_invalid_datagram(config.dump_path_for_invalid_datagram, alldata)
         except sqlite3.OperationalError as err:
             logger.error("Database error: %s", str(err))