Fix some warnings about missing return statements

Author: d-frey

include/tao/json/events/cbor/grammar.hpp

@@ -94,7 +94,10 @@ namespace tao
                      case major::OTHER:
                         return match_other( in, consumer );
                   }
+                  // LCOV_EXCL_START
                   assert( false );
+                  return false;
+                  // LCOV_EXCL_STOP
                }
 
                template< typename Input >

include/tao/json/events/msgpack/to_stream.hpp

@@ -160,7 +160,7 @@ namespace tao
 
                void end_array()
                {
-                  assert( false );
+                  assert( false );  // LCOV_EXCL_LINE
                }
 
                void end_array( const std::size_t ) noexcept
@@ -199,7 +199,7 @@ namespace tao
 
                void end_object()
                {
-                  assert( false );
+                  assert( false );  // LCOV_EXCL_LINE
                }
 
                void end_object( const std::size_t ) noexcept

include/tao/json/internal/jaxn/action.hpp

@@ -79,7 +79,10 @@ namespace tao
                   if( ( 'A' <= c ) && ( c <= 'F' ) ) {
                      return c - 'A' + 10;
                   }
+                  // LCOV_EXCL_START
                   assert( false );
+                  return false;
+                  // LCOV_EXCL_STOP
                }
 
                template< typename Input, typename Consumer >

src/test/json/unhex.hpp

@@ -24,7 +24,10 @@ namespace tao
             if( ( 'A' <= c ) && ( c <= 'F' ) ) {
                return c - 'A' + 10;
             }
+            // LCOV_EXCL_START
             assert( false );
+            return 0;
+            // LCOV_EXCL_STOP
          }
 
          inline std::string unhex( const std::string& data )