bugfix(damage): Fix kill flag version check in DamageInfoInput::xfer

[bobtista]

• Fixes Generals crashes loading a retail compatible save when retail compatibility is disabled #3298
• Recovers the Damage.cpp part of the closed bugfix(saveload): Fix silent crash loading old saves under RETAIL_COMPATIBLE_XFER_SAVE=0 #2922

DamageInfoInput::xfer checks currentVersion before reading m_kill:

// kill no matter what (old versions default to FALSE).
if( currentVersion >= 2 )
{
    xfer->xferBool( &m_kill );
}

currentVersion is 1 in a retail compatible Generals build and 3 otherwise. A Generals build with retail compatibility off reads a byte that a version 1 record does not have, and every field after it is off by one. ActiveBody::xfer transfers a DamageInfo for every object, so the load dies on the first one.

Now it checks version. The m_damageFXOverride read above it and the version 3 block below it already do. Save output does not change, version and currentVersion are equal when saving.

Measured on USA01. Saved at frame 1903 with a retail compatible build, then loaded that save with a build configured RTS_BUILD_OPTION_RETAIL_COMPATIBLE_GAME=OFF, once before and once after this change. The retail compatible build writes version 1 damage records, same as retail 1.08.

Before the change the load hits an access violation on Xfer Object GLATankScorpion id=2363, the first object in the file. After it, all 3781 objects load and the game runs on to frame 2100 and saves again. Same tree, same build directory, this line is the only difference between the two exes.

Zero Hour saves are always version 3, so nothing changes there.

Todo:

• A version 1 save loads in a build with retail compatibility disabled
• Save output is unchanged
• Replicate to Generals — N/A, shared Core code