Fix potential OOB access in sdp_db.cc

Owing to an improper bounds check, a buffer in SDP_AddAttributeToRecord
can underflow and lead to OOC access with the proper inputs.

Add the correct bounds check.

Bug: 272783039
Test: atest bluetooth_test_gd_unit
Tag: #security
Ignore-AOSP-First: Security
Change-Id: I9ee55ef36ea5eb55de1efc704b68ce7c07c7a604