Bug #52131: SET and ENUM stored endian-dependent in binary log

Post-Push fix, DBUG build broken on freebsd7

sql/field.cc:8456: warning: control reaches end of non-void function

sql/field.cc:
  Return NULL to keep compiler happy.

sql/field.cc

@@ -8408,6 +8408,8 @@ uchar *Field_enum::pack(uchar *to, const uchar *from,
   default:
     DBUG_ASSERT(0);
   }
+  MY_ASSERT_UNREACHABLE();
+  DBUG_RETURN(NULL);
 }
 
 const uchar *Field_enum::unpack(uchar *to, const uchar *from,
@@ -8430,6 +8432,8 @@ const uchar *Field_enum::unpack(uchar *to, const uchar *from,
   default:
     DBUG_ASSERT(0);
   }
+  MY_ASSERT_UNREACHABLE();
+  DBUG_RETURN(NULL);
 }