fix: disallow null char at the end of input

since std::string and ""_toml literal actually does not include null
char, we don't need to check if the last char is null or not

toml/literal.hpp

@@ -87,6 +87,7 @@ operator"" _toml(const char* str, std::size_t len)
     ::toml::detail::location loc(
             std::string("TOML literal encoded in a C++ code"),
             std::vector<char>(str, str + len));
+    // literal length does not include the null character at the end.
     return literal_internal_impl(std::move(loc));
 }
 

toml/parser.hpp

@@ -2209,13 +2209,6 @@ parse(std::istream& is, const std::string& fname = "unknown file")
     std::vector<char> letters(static_cast<std::size_t>(fsize));
     is.read(letters.data(), fsize);
 
-    // remove null character if exists
-    while(!letters.empty() && letters.back() == '\0')
-    {
-        letters.pop_back();
-    }
-    assert(letters.empty() || letters.back() != '\0');
-
     // append LF.
     // Although TOML does not require LF at the EOF, to make parsing logic
     // simpler, we "normalize" the content by adding LF if it does not exist.