Some functions, like `patch_init_rc()`, treat buffers read into memory
as a string instead of a byte buffer. Since the buffers weren't
NULL-terminated, this resulted in out-of-bounds reads and caused crashes
in certain conditions.
THis commit updates fd_full_read() to always NULL-terminate the buffers
so that they can be treated as strings when working with text files.
Signed-off-by: Andrew Gunnerson <andrewgunnerson@gmail.com>
