Fix length of descriptor field when reading debug info.

TypeIndex is a 16-bit value, and storing kDexNoIndex (0xFFFFFFFF) caused
a failure in a dcheck on the bounds of the value.

Bug: 37287051
Test: mm -j31 test-art-host-gtest-dex_file_test
Change-Id: I8344ea126b044563b9a25e1303b7e3e7124ef86f