Work around cid#1328486

...claiming that "right shifting v by more than 15 bits always yields zero,"
apparently diagnosing an instanatiation of the template for T = unsigned short.

Change-Id: I7c210ff17e4aef8f0e703cc30518f3420e67e7c1

basebmp/inc/metafunctions.hxx

@@ -214,10 +214,11 @@ template< typename T > inline T shiftRight( T v, int shift )
     static_assert(
         std::is_unsigned<T>::value,
         "must be unsigned for promotedBits and the below ': 0' to be correct");
-    auto const promotedBits = std::numeric_limits<decltype(+T())>::digits;
+    using Promoted = decltype(+T());
+    auto const promotedBits = std::numeric_limits<Promoted>::digits;
     return shift >= 0
-        ? shift < promotedBits ? v >> shift : 0
-        : -shift < promotedBits ? v << (-shift) : 0;
+        ? shift < promotedBits ? Promoted(v) >> shift : 0
+        : -shift < promotedBits ? Promoted(v) << (-shift) : 0;
 }
 
 } // namespace basebmp