Avoid nil pointer when reading logs of a just terminated container.  Hit this when following logs of a container restarted with a health check:  ``` panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x168771e]
Avoid nil pointer when reading logs of a just terminated container. 
Hit this when following logs of a container restarted with a health check: 
```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x168771e]

goroutine 1 [running]:
github.com/docker/compose-cli/aci.getACIContainerLogs(0x2d85260, 0xc000526c60, 0xc0001465a0, 0x24, 0xc0004f4da0, 0xa, 0xc0004f4db0, 0x7, 0x7ffeefbffab2, 0xb, ...)
	github.com/docker/compose-cli/aci/aci.go:285 +0x1fe
github.com/docker/compose-cli/aci.streamLogs(0x2d85260, 0xc000526c60, 0xc0001465a0, 0x24, 0xc0004f4da0, 0xa, 0xc0004f4db0, 0x7, 0x7ffeefbffab2, 0xb, ...)
	github.com/docker/compose-cli/aci/aci.go:297 +0x2e5
```

Signed-off-by: Guillaume Tardif <fdb6d90518c0d82cc6b9e4626ba807cce7a41bc7@docker.com>
docker/compose,docker/compose,docker/compose