Avoid valgrind memory leak false positive in processInlineBuffer().

zmalloc(0) cauesd to actually trigger a non-zero allocation since with
standard libc malloc we have our own zmalloc header for memory tracking,
but at the same time the returned pointer is at the end of the block and
not in the middle. This triggers a false positive when testing with
valgrind.

When the inline protocol args count is 0, we now avoid reallocating
c->argv, preventing the issue to happen.
Merge remote-tracking branch 'origin/unstable' into unstable
Document redis-cli --stat in --help output.