Fix null pointer dereference in auditParse

There is an issue in LogAudit::auditParse where
android::uidToName(uid) crashes with a null pointer dereference.
Include a null check on the value before passing it on.

Bug: 120043607
Test: End-to-end test with syzkaller as per instructions in bug.
Change-Id: Ic0ac5c3003fcd289ec156ce63fbd668413763429
diff --git a/logd/LogAudit.cpp b/logd/LogAudit.cpp
index fc8c960..18d5287 100644
--- a/logd/LogAudit.cpp
+++ b/logd/LogAudit.cpp
@@ -165,9 +165,14 @@
         bug_num->assign("");
     }
 
+    // Ensure the uid name is not null before passing it to the bug string.
     if (uid >= AID_APP_START && uid <= AID_APP_END) {
-        bug_num->append(" app=");
-        bug_num->append(android::uidToName(uid));
+        char* uidname = android::uidToName(uid);
+        if (uidname) {
+            bug_num->append(" app=");
+            bug_num->append(uidname);
+            free(uidname);
+        }
     }
 }