Summarized Changelog:

• Fix an out-of-bounds read of maximal two bytes for truncated RVA2 frames.
• Fix an invalid write of one zero byte for empty ID3v2 frames that demand de-unsyncing.
• Correct preprocessor syntax in mangle.h, no #error in a #define line.
• Reset the flag for having a frame to decode before trying to parse a new one. This prevents very unkind behaviour (crashes) when combinging mpg123_scan() with decoding later on for damaged streams that have a mixture of different MPEG versions.

• Rebuild gzdoom against this version.
• Use mp3gain on a demo file using this update.