str: preallocate more single-char strings
str: preallocate more single-char strings

One (heavy) consumer saw a 11% reduction of allocations:

cache                        buf     buf     buf     buf  memory     alloc alloc
name                        size  in use  in ptc   total  in use   succeed  fail
------------------------- ------ ------- ------- ------- ------- --------- -----
str-cache (before)            24    5256       -    5508    216K    595787     0
str-cache (after)             24    5240       -    5406    212K    530102     0

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc