kdeinit5 overwrites argv, which in turn results in /proc/self/cmdline
being overwritten. It seems that this is done in a way that does not
necessarily guarantee that /proc/self/cmdline will end up NUL-terminated.

However, g_file_get_contents() is documented to fill a buffer of size
len + 1, where buffer[len] == '\0', even if the file's actual contents
(from buffer[0] to buffer[len-1] inclusive) did not include a NUL;
so we can safely relax this assertion slightly.

Resolves: #1923


Signed-off-by: Simon McVittie <smcv@collabora.com>