help assimp find vcpkg's copy of zlib so it does not build its own

[mcgoo]

Without this, assimp uses its internal copy of zlib so the port installs zlibstatic.lib.

[alexkaratarakis]

Thanks! I bumped the version in the CONTROL file.

[ras0219-msft]

After further investigation, I discovered the true culprit is that assimp was overwriting the CMAKE_PREFIX_PATH variable, preventing it from finding any libraries inside vcpkg. I've pushed a fix for that as 4.0.1-2.

Note that the fix in 4.0.1-1 causes the release zlib.lib to be linked in Debug mode, so I recommend updating to 4.0.1-2 instead.