Fixes fallthrough in lexer on initial bytes of Byte order mark (\xEF), but not the following ones.

src/Parser/Lexer/Lexer.cpp

@@ -250,6 +250,8 @@ namespace MalachScript::Parser {
                     Progress(2);
                     return Create<LexTokenImpl<LexTokenKind::Whitespace>>(TextSpan(start, start + 3));
                 }
+                LogError(Diagnostics::DiagnosticType::UnknownToken, TextSpan(start, start + 1));
+                return Create<LexTokenImpl<LexTokenKind::Unknown>>(TextSpan(start, start + 1));
             }
             case u8'0':
             case u8'1':