Add a default class to the byte transcoder state switch. (#298)

Author: paulhuggett

include/icubaby/icubaby.hpp

@@ -1376,6 +1376,8 @@ template <ICUBABY_CONCEPT_UNICODE_CHAR_TYPE ToEncoding> class transcoder<std::by
 
     case states::run_32be_byte3:
     case states::run_32le_byte3: dest = this->run32 (value, dest); break;
+
+    default: assert (false && "Unknown byte transcoder state");
     }
     return dest;
   }