reject directory entries in the noalloc entry readers

[jmestwa-coder]

zip_entry_read and zip_entry_fread reject a directory entry, but the two no-alloc readers don't:

• zip_entry_noallocread returns the declared uncomp_size while miniz's extractor reports success without ever writing buf or checking bufsize (it short-circuits directory entries first), so a crafted "a/" deflate entry with a large uncomp_size reports far more bytes than were written into the caller's fixed buffer
• zip_entry_noallocreadwithoffset takes the same entry through extract_to_heap and copies a window out of the unwritten heap block, leaking uninitialized memory
• added the is_file_a_directory guard both readers already use, returning ZIP_EINVENTTYPE, plus a regression test

[kuba--]

zip_entry_noallocreadwithoffset() checks the offset before checking whether the entry is a directory:

if (offset >= (size_t)zip->entry.uncomp_size)
  return ZIP_EINVAL;
/* Later: */
if (mz_zip_reader_is_file_a_directory(...))
  return ZIP_EINVENTTYPE;

Therefore, for a directory:

offset < declared uncomp_size → ZIP_EINVENTTYPE
offset >= declared uncomp_size → ZIP_EINVAL

Moving the directory check earlier would make every directory call consistently return ZIP_EINVENTTYPE.

[jmestwa-coder]

good point, moved the directory check ahead of the offset check so a directory entry returns ZIP_EINVENTTYPE regardless of offset. added an assertion with offset past the declared size to lock that in.