playlist/cue/parser: use lambda to fix ambiguous overload

On Windows, there is an IsWhitespaceOrNull() overload with TCHAR, and
the compiler doesn't know which one to pass to std::find_if().

src/playlist/cue/CueParser.cxx

@@ -32,7 +32,7 @@ cue_next_word(StringView &src) noexcept
 	assert(!IsWhitespaceNotNull(src.front()));
 
 	auto end = std::find_if(src.begin(), src.end(),
-				IsWhitespaceOrNull);
+				[](char ch){ return IsWhitespaceOrNull(ch); });
 	StringView word(src.begin(), end);
 	src = src.substr(end);
 	return word;