encoding non-record types results in panic

[rogpeppe]

This code panics because the newAzTypeInfo code doesn't recognize that a non-record type might have entries.

	type R struct {
		A int
	}
	avro.Marshal(&R{13})

panic: runtime error: index out of range [0] with length 0 [recovered]
	panic: runtime error: index out of range [0] with length 0

goroutine 42 [running]:
testing.tRunner.func1.1(0x648c80, 0xc0000a0820)
	/home/rog/go/src/testing/testing.go:942 +0x3d0
testing.tRunner.func1(0xc0002018c0)
	/home/rog/go/src/testing/testing.go:945 +0x3f9
panic(0x648c80, 0xc0000a0820)
	/home/rog/go/src/runtime/panic.go:967 +0x15d
github.com/heetch/avro.typeEncoderUncached(0xc000056300, 0x6b5b20, 0xc00020dac0, 0x6b6a40, 0x5fefa0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	/home/rog/src/heetch/avro/encode.go:181 +0x1725
github.com/heetch/avro.typeEncoder0(0xc000056300, 0x0, 0x0, 0x6b6a40, 0x5fefa0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	/home/rog/src/heetch/avro/encode.go:121 +0x146
github.com/heetch/avro.marshalAppend(0xc000056300, 0x0, 0x0, 0x0, 0x5fefa0, 0xc0000f6b48, 0x16, 0x0, 0x0, 0x0, ...)
	/home/rog/src/heetch/avro/encode.go:41 +0xde
github.com/heetch/avro.Marshal(0x5fefa0, 0xc0000f6b48, 0x453d99, 0x72902ea491ca, 0x2c540c30, 0x2c540c300000000f, 0x5e2ecb98, 0xc000036770)
	/home/rog/src/heetch/avro/encode.go:31 +0xc5
github.com/heetch/avro_test.TestGoTypeEncodeWithPointer(0xc0002018c0)
	/home/rog/src/heetch/avro/gotype_test.go:273 +0x8c
testing.tRunner(0xc0002018c0, 0x670460)
	/home/rog/go/src/testing/testing.go:993 +0xdc
created by testing.(*T).Run
	/home/rog/go/src/testing/testing.go:1044 +0x357

goroutine 1 [chan receive]:
testing.(*T).Run(0xc0002018c0, 0x666eaa, 0x1b, 0x670460, 0x483e01)
	/home/rog/go/src/testing/testing.go:1045 +0x37e
testing.runTests.func1(0xc000158000)
	/home/rog/go/src/testing/testing.go:1286 +0x78
testing.tRunner(0xc000158000, 0xc000047e10)
	/home/rog/go/src/testing/testing.go:993 +0xdc
testing.runTests(0xc00000c220, 0x82c7a0, 0x13, 0x13, 0x0)
	/home/rog/go/src/testing/testing.go:1284 +0x2a7
testing.(*M).Run(0xc000156000, 0x0)
	/home/rog/go/src/testing/testing.go:1201 +0x15f
main.main()
	_testmain.go:86 +0x135
go: exit 1
exit status 2
FAIL	github.com/heetch/avro	0.012s