fix(activesync): harden base64 URI decoding for GET requests

[TDannhauer]

Summary

• Harden Horde_ActiveSync_Utils::decodeBase64() against malformed QUERY_STRING values
• Add missing EAS command codes (GetHierarchy through Find)
• Skip DeviceType normalization when decoding fails

Motivation

Non-ActiveSync requests hitting the ActiveSync endpoint with a long enough QUERY_STRING were base64-decoded as garbage, producing PHP warnings for unknown command bytes, failed unpack() calls, and undefined DeviceType access in getGetVars().

Changes

• Validate strict base64 decoding, header length, known command codes, and length-prefixed fields before unpack()
• Return an empty array instead of partial invalid results
• Guard DeviceType normalization with ?? '' and only accept decoded results when Cmd is present
• Add unit test for invalid payloads

Test plan

• vendor/bin/phpunit --bootstrap vendor/autoload.php vendor/horde/activesync/test/unit/Horde/ActiveSync/UtilsTest.php
• Confirm ActiveSync device sync still works with real base64-encoded URIs