Failure to process ServerCertificate in mender.conf if no trust roots are present on the system

If no trust roots are installed on the system and ServerCertificate is present then mender client fails with:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1090f4]

goroutine 1 [running]
panic(0x2d4530, 0x1071e008)
/sources/go/src/runtime/panic.go:500 +0x33c
crypto/x509.(*CertPool).AddCert(0x0, 0x10769b00)
/sources/go/src/crypto/x509/cert_pool.go:74 +0x74
crypto/x509.(*CertPool).AppendCertsFromPEM(0x0, 0x10b8aa5f, 0x254, 0x454, 0x600)
/sources/go/src/crypto/x509/cert_pool.go:113 +0x148
github.com/mendersoftware/mender/client.loadServerTrust(0x0, 0x0, 0x0, 0x0, 0x10711620, 0x16, 0x0, 0x32, 0x0, 0x0)
/root/go/src/github.com/mendersoftware/mender/client/client.go:204 +0x174
github.com/mendersoftware/mender/client.newHttpsClient(0x0, 0x0, 0x0, 0x0, 0x10711620, 0x16, 0x0, 0x6, 0x0, 0x0)
/root/go/src/github.com/mendersoftware/mender/client/client.go:147 +0xa4
github.com/mendersoftware/mender/client.New(0x0, 0x0, 0x0, 0x0, 0x10711620, 0x16, 0x0, 0x0, 0x0, 0x0)
/root/go/src/github.com/mendersoftware/mender/client/client.go:115 +0x3f8
main.NewMender(0x1079ae20, 0x4, 0x30c2f0, 0x10, 0x0, 0x0, 0x0, 0x0, 0x0, 0x1079ae90, ...)
/root/go/src/github.com/mendersoftware/mender/mender.go:192 +0x1d4
main.doBootstrapAuthorize(0x10762780, 0x10712440, 0x0, 0x0)
/root/go/src/github.com/mendersoftware/mender/main.go:284 +0xe8
main.doMain(0x1070c158, 0x1, 0x1, 0x0, 0x0)
/root/go/src/github.com/mendersoftware/mender/main.go:415 +0x5f0
main.main()
/root/go/src/github.com/mendersoftware/mender/main.go:434 +0x7c

The issue appears that x509.SystemCertPool() may return invalid certs while issuing no error (perhaps it is the issue with x509 in go - will dig a bit deeper). Attempt to append certificates to invalid pool causes the error.