addrman: Add missing lock in Clear() (CAddrMan)

The variable vRandom is guarded by the mutex cs.

src/addrman.h

@@ -455,6 +455,7 @@ class CAddrMan
 
     void Clear()
     {
+        LOCK(cs);
         std::vector<int>().swap(vRandom);
         nKey = GetRandHash();
         for (size_t bucket = 0; bucket < ADDRMAN_NEW_BUCKET_COUNT; bucket++) {