GHSA-q579-9wp9-gfp2: Window can read out of bounds if Read instance returns more bytes than buffer size

rdiff performs a diff of two provided strings or files. As part of its reading code it uses the return value of a Read instance to set the length of its internal character vector.

If the Read implementation claims that it has read more bytes than the length of the provided buffer, the length of the vector will be set to longer than its capacity. This causes rdiff APIs to return uninitialized memory in its API methods.