use memmove instead of memcpy

src/bufio.h

@@ -153,7 +153,7 @@ inline int IBuf<bufsiz>::peek(size_t count) {
 		return buf_[idx_ + offset];
 	} else {
 		len_ -= idx_;
-		memcpy(buf_, buf_ + idx_, len_);
+		memmove(buf_, buf_ + idx_, len_);
 		idx_ = 0;
 		len_ += is_.read(buf_ + len_, sizeof(buf_) - len_);
 		if (len_ <= offset) {