Fix silly icc remark #2259

Another stupid remark to quiet out:

remark #2259: non-pointer conversion from "int" to "UINT16={unsigned short}"
may lose significant bits

In this case icc always converts to an integer the result of a shift operation
if the bit size of the operand is smaller, hence the warning when assignin
back to n.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/book.cpp

@@ -511,7 +511,7 @@ Book& Book::operator>>(T& n) {
   n = 0;
 
   for (size_t i = 0; i < sizeof(T); i++)
-      n = (n << 8) + (T)bookFile.get();
+      n = T((n << 8) + bookFile.get());
 
   return *this;
 }