Check some return values when it makes sense to do so.

Fixes CID #965877 #1111761 #1111762 #1111764.
Simplify string handling to avoid possible null dereference.

Fixes CID #1111767.
CDDAReader: Use _byteswap_ushort when possible.

Fixes CID #966012 #966205.
Document some switch cases that intentionally don't end with a break statement.

Fixes CID #966019 #966020.
Avoid a potential (though unlikely) memory leak.

Fixes CID #1111770.
Check that CAutoVectorPtr::Allocate succeeded before using the memory.

Fixes CID #965879 #1111760.
Always check IMediaSample::GetPointer return value.

Fixes CID #965883 #965884.
DVBSub/PGSSub: Add more error checking when parsing composition object.

Fixes CID #971508.
Initialize a variable.

Fixes CID #1111779.
Remove some dead code.

Fixes CID #965946.
Improve the Get(Cur)DispMode and SetDispMode functions.

Fixes CID #966222.