example_18-01_from_disk readFilenames problem

[j32u4ukh]

The code of readFilenames for windows users has two problem as below:

1. When dealing with the situation no files found, will cause no return value problem.

...
if ((dir = FindFirstFile((directory + "/*").c_str(), &file_data)) == INVALID_HANDLE_VALUE)
        return;  // no files found
    do {
...

2. Add full_file_name into vector of filenames, cause the program can not find files.

    ...
        filenames.push_back(full_file_name);
    } while (FindNextFile(dir, &file_data));
    ....