Fix buffer overflow error in cel3ds, improve error handling

[ajtribick]

I noticed a potential buffer overflow error in the readString function in 3dsread.cpp: if the string is 1024 characters or longer, the terminating zero byte is not written and the string constructor from const char* will therefore read beyond the end of the buffer.

The rest of the loader functionality was in my opinion far too trusting that the input files are not malformed. I've therefore added various error checking that was missing, including verifying that the stream is in a good state after attempting to read data, and consistency checks that the expected amount of data has been read. I also replaced the void pointer usage with templates to ensure better type safety, and switched to using std::make_unique rather than new to simplify cleanup on the error path.

So far I've checked that the Apollo 11 and Mir models still load.

[ajtribick]

The code analysis report for the comma operator in matrix initialization is a known issue: https://trac.cppcheck.net/ticket/10518

As for the "Check buffer boundaries if used in a loop including recursive loops" - I genuinely don't know what it wants me to do here. The call to read is using the size of the buffer defined immediately beforehand. I think this is the same issue as david-a-wheeler/flawfinder#59

[375gnu]

sometimes c++ is too stupid. but let's roll

[375gnu]

@ajtribick we usually merge own PRs ourselves so feel free to merge this if you consider it ready.