ws2_32: Pass correct buffer length to WS_inet_ntop (Coverity).

dlls/ws2_32/socket.c

@@ -7663,12 +7663,14 @@ INT WINAPI WSAAddressToStringA( LPSOCKADDR sockaddr, DWORD len,
     case WS_AF_INET6:
     {
         struct WS_sockaddr_in6 *sockaddr6 = (LPSOCKADDR_IN6) sockaddr;
+        size_t slen;
 
         buffer[0] = 0;
         if (len < sizeof(SOCKADDR_IN6)) return SOCKET_ERROR;
         if ((sockaddr6->sin6_port))
             strcpy(buffer, "[");
-        if (!WS_inet_ntop(WS_AF_INET6, &sockaddr6->sin6_addr, buffer+strlen(buffer), sizeof(buffer)))
+        slen = strlen(buffer);
+        if (!WS_inet_ntop(WS_AF_INET6, &sockaddr6->sin6_addr, &buffer[slen], sizeof(buffer) - slen))
         {
             SetLastError(WSAEINVAL);
             return SOCKET_ERROR;