arrayfuncs: fix read of uninitialized mem

This patch fixes a read of uninitialized memory in array_out(). The code
was previously doing a strlen() on a stack-allocated char array that,
under some code paths, had never been assigned to. The problem doesn't
appear in REL7_4_STABLE, so there's no need for a backport.

I fixed it by initializing dims_str[0] to '\0' circa line 1018 in
current sources. While doing so I couldn't resist the temptation to fix
a few of arrayfunc.c's crimes against good programming practise, so the
attached patch includes some additional cosmetic improvements. If people
prefer I can just apply the bugfix to HEAD, and save the cleanup till we
branch for 8.1. Comments?

Barring any objections, I'll apply the patch within 24 hours.

-Neil