pretty: don't panic if we can't call Interface on a value.
pretty: don't panic if we can't call Interface on a value.

Change-Id: Iae36134796f85018bec2b7b9cb0cd4cc3390fa02
Reviewed-on: https://code-review.googlesource.com/8770
Reviewed-by: Jun Mukai <7519e7503d434ad998e9a85ea6f0976705697504@google.com>

michael-grosshans/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,michael-grosshans/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go