fix(content): Decode IPLS/TIPL/TMCL with odd value count gracefully

[Holzhaus]

This might be an option to fix decoding errors due to broken IPLS/TIPL/TMCL frames. See #147 for details.

Note: The big downside of this solution is that applications have no way to distinguish a tag with a valid TIPL frame where the last even value is empty from a tag with an invalid TIPL frame where the last even value is missing anymore.
If you wanted to bui.d a tool that checks if your tags are valid, you couldn't use rust-id3 anymore. If this should be possible, we'd have to go for options 2/3 described in #147 (comment).

Using this branch, the sample file from #147 can be decoded successfully:

$ cargo run --example id3info sample.mp3
# ID3 ID3v2.4 - 35 frames
TIT2="Wily's Castle"
TPE1="RushJet1"
TRCK="17/28"
TALB="Mega Man 2 Remade"
TPOS="1/1"
TDRC="2014-12-01"
TCON="8-Bit Electronic"
TBPM="0"
TCMP="0"
TLAN="eng"
USLT:[XXX]=""
TPE2="RushJet1"
TSOP="RushJet1"
TIPL:arranger=""
TDOR="2014-12-01"
TXXX:Script="Latn"
TMED="Digital Media"
TXXX:Artist Credit="RushJet1"
TXXX:MP3GAIN_MINMAX="063,208"
TXXX:ALBUMARTISTSORT="RushJet1"
TXXX:MP3GAIN_UNDO="+002,+002,N"
TXXX:Album Artist Credit="RushJet1"
COMM:[eng]="Visit http://rushjet1.com"
TXXX:MusicBrainz Album Status="Official"
TXXX:MusicBrainz Album Release Country="XW"
TXXX:MusicBrainz Album Id="6cda3c13-80b7-49a4-b8ac-889565442f94"
UFID:http://musicbrainz.org=b"ef471528-ee72-49a7-b0d4-500a6034ea6e"
TXXX:MusicBrainz Release Group Id="570518df-14de-4b4d-9c97-e02a58d057b1"
TXXX:MusicBrainz Release Track Id="c79faf7f-43b8-4ba3-b553-3f931b5f9bd8"
COMM:iTunNORM[eng]=" 000003DA 000003DA 000009A2 000009A2 00000000 00000000 00005A81 00005A81 00000000 00000000"
APIC:Front cover=<image, image/jpeg, description "", 40510 bytes>
TXXX:REPLAYGAIN_TRACK_GAIN="-2.48 dB"
TXXX:REPLAYGAIN_TRACK_PEAK="0.715942"
TXXX:REPLAYGAIN_ALBUM_GAIN="-2.03 dB"
TXXX:REPLAYGAIN_ALBUM_PEAK="0.851807"

[polyfloyd]

Nice!

This seems like a good solution. I am not super concerned about being able to check tags for validity. ID3 is an old standard and there is plenty of mangled data out there. Being able to read as much as possible is preferred.