[PATCH] strbuf: stop out-of-boundary warnings from Coverity

It usually goes like this

    strbuf sb = STRBUF_INIT;
    if (!strncmp(sb.buf, "foo", 3))
       printf("%s", sb.buf + 3);

Coverity thinks that printf() can be executed, and because initial sb.buf only has one character (from strbuf_slopbuf), sb.buf + 3 is out of bound. What it does not recognize is strbuf_slopbuf[0] is always (*) zero. We always do some string comparison before jumping ahead to "sb.buf + 3" and those operations will stop out of bound accesses.

Just make strbuf_slopbuf[] large enough to keep Coverity happy. If it's happy, we'll have cleaner defect list and better chances of spotting true defects.

(*) It's not entirely wrong though. Somebody may do sb.buf[0] = 'f'
    right after variable declaration and ruin all unused strbuf.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 There are lots of false warnings like this from Coverity. I just
 wanted to kill them off so we can spot more serious problems easier.
 I can't really verify that this patch shuts off those warnings
 because scan.coverity.com policy does not allow forks.

 I had another patch that avoids corrupting strbuf_slopbuf, by putting
 it to .rodata section. The patch is more invasive though, because
 this statement buf.buf[buf.len] = '\0' now has to make sure buf.buf
 is not strbuf_slopbuf. It feels safer, but probably not enough to
 justify the change.

 strbuf.c | 5 +++++
 1 file changed, 5 insertions(+)