Using mg_bzero to cleanup memory in mg_close_conn()

mongoose.h

@@ -1016,6 +1016,7 @@ struct mg_str mg_unpacked(const char *path);  // Packed file as mg_str
 #define assert(x)
 #endif
 
+void mg_bzero(volatile unsigned char *buf, size_t len);
 void mg_random(void *buf, size_t len);
 char *mg_random_str(char *buf, size_t len);
 uint16_t mg_ntohs(uint16_t net);