🐛 Fix bit_ceil() to return 1 for input 0 as per specification

include/boost/core/bit.hpp

@@ -703,7 +703,7 @@ BOOST_CXX14_CONSTEXPR inline boost::uint32_t bit_ceil_impl( boost::uint32_t x )
 {
     if( x == 0 )
     {
-        return 0;
+        return 1;
     }
 
     --x;
@@ -723,7 +723,7 @@ BOOST_CXX14_CONSTEXPR inline boost::uint64_t bit_ceil_impl( boost::uint64_t x )
 {
     if( x == 0 )
     {
-        return 0;
+        return 1;
     }
 
     --x;