DirectoryBlob: Don't add DiscContents with size 0

Having DiscContents with size 0 would mean that some DiscContents
might not get added to the std::set because of them comparing
identically to another DiscContent.

This replaces an older piece of code in WriteDirectory that ensures
that no two files have the same starting offset. (We now care about
the ending offset, not the starting offset. The new solution both
ensures that no two files have the same ending offset and that no
two files have the same starting offset.)

Source/Core/DiscIO/DirectoryBlob.cpp

@@ -122,11 +122,13 @@ bool DiscContent::Read(u64* offset, u64* length, u8** buffer) const
 
 void DiscContentContainer::Add(u64 offset, u64 size, const std::string& path)
 {
+  if (size != 0)
     m_contents.emplace(offset, size, path);
 }
 
 void DiscContentContainer::Add(u64 offset, u64 size, const u8* data)
 {
+  if (size != 0)
     m_contents.emplace(offset, size, data);
 }
 
@@ -761,7 +763,7 @@ void DirectoryBlobPartition::WriteDirectory(const File::FSTEntry& parent_entry,
       m_contents.Add(*data_offset, entry.size, entry.physicalName);
 
       // 32 KiB aligned - many games are fine with less alignment, but not all
-      *data_offset = Common::AlignUp(*data_offset + std::max<u64>(entry.size, 1ull), 0x8000ull);
+      *data_offset = Common::AlignUp(*data_offset + entry.size, 0x8000ull);
     }
   }
 }