Ignore getheaders requests when not synced.

src/main.cpp

@@ -4174,6 +4174,9 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 
         LOCK(cs_main);
 
+        if (IsInitialBlockDownload())
+            return true;
+
         CBlockIndex* pindex = NULL;
         if (locator.IsNull())
         {