`plutil` does not handle the key path correctly when there is a nesting key path

[biaocy]

plutil/Libraries/plist/Tools/plutil.cpp

Lines 616 to 617 in affa752

	end = path.find('.', end);
	std::string key = (end != std::string::npos ? path.substr(start, end - start) : path.substr(start));

The second parameter to path.find should be start, otherwise it will always find the first ., and the sub-key will be path.substr(first-dot-index, -1), cause the program to report error: invalid key path