Fix potential interger overflow when parsing vendor response

Add check for str_len to prevent potential OOB read in vendor response.

Bug: 205570663
Tag: #security
Test: net_test_stack:StackAvrcpTest
Ignore-AOSP-First: Security
Change-Id: Iea2c3e17c2c8cc56468c4456822e1c4c5c15f5bc
Merged-Id: Iea2c3e17c2c8cc56468c4456822e1c4c5c15f5bc