Various little fixes found by coccinelle

The coccinellery repository provides many little semantic patches to fix common problems in the code. The number of semantic patches in the coccinellery repository is high and most of the semantic patches apply only for Linux, so it doesn't make sense to run them on regular basis as the processing takes a lot of time.

The list of issue found in BIND 9, by no means complete, includes:

• double assignment to a variable
• continue at the end of the loop
• double checks for NULL
• useless checks for NULL (cannot be NULL, because of earlier return)
• using 0 instead of NULL
• useless extra condition (if (foo) return; if (!foo) { ...; })
• removing & in front of static functions passed as arguments