When printing out an ASN.1 structure, if the type is an item template don't
fall through and attempt to interpret as a primitive type.

(Imported from upstream's 5dc1247a7494f50c88ce7492518bbe0ce6f124fa.)

Change-Id: Ica39757792cbf3f83879953b67838927ddbdb809
Reviewed-on: https://boringssl-review.googlesource.com/4009
Reviewed-by: Adam Langley <agl@google.com>

The call to asn1_do_adb can return NULL on error, so we should check the
return value before attempting to use it.

(Imported from upstream's 34a7ed0c39aa3ab67eea1e106577525eaf0d7a00.)

Change-Id: Ia43cdc73b5f1d16e6fc907b5aaf13c9df5a9958c
Reviewed-on: https://boringssl-review.googlesource.com/4007
Reviewed-by: Adam Langley <agl@google.com>

This change fixes a number of build warnings.

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)