Check whether files could be opened before writing; resolves #542 #376

Job	Run time
windows-msvc-shared (AVRO)	6m 35s
windows-msvc-shared (FLEXBUFFERS)	5m 23s
windows-msvc-shared (CAPNPROTO)	7m 33s
windows-msvc-shared (PARQUET)	39m 7s
windows-msvc-shared (MSGPACK)	4m 14s
windows-msvc-shared (TOML)	3m 59s
windows-msvc-shared (YAML)	4m 3s
windows-msvc-shared (CBOR)	8m 21s
windows-msvc-shared (XML)	3m 50s
windows-msvc-shared (UBJSON)	3m 6s
windows-msvc (UBJSON)	1s
windows-msvc (JSON)	1s
windows-msvc (PARQUET)	1s
windows-msvc (XML)	1s
windows-msvc (CBOR)	1m 15s
windows-msvc (FLEXBUFFERS)	1s
windows-msvc (benchmarks)	1m 15s
windows-msvc (MSGPACK)	1m 15s
windows-msvc (CAPNPROTO)	1s
windows-msvc (AVRO)	1s
windows-msvc (YAML)	1s
windows-msvc (TOML)	1m 15s
windows-msvc-shared (JSON)	10m 21s
	1h 41m 40s

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