Initialise padding after the file buffer

[wcawijngaards]

The change initializes the padding after the file buffer. Otherwise checkers report use of uninitialised memory from those bytes. It zeroes the block size after the fread, so it does not have to wipe the entire buffer. For strings, that means the library caller would have to initialize them.

[lemire]

Alternatively, you can silence the sanitizer warnings.

[wcawijngaards]

That is true, tools have options for that. I have not used those before. I think the zero of the padding is the best choice, it is not expensive because only padding per file read, of a couple bytes per 16Kb read, and also provides actual initialization, in a defense in depth sense a good measure. If it was expensive, it can get a configure option for maintenance mode and clean debug output.