Fix interned strings buffer check if 0 free bytes

Fix interned strings buffer check if 0 free bytes

With #32902 it was meant to be avoided to recommend raising the interned strings buffer size above a quarter of the total OPcache size. This works as long as there is at least 1 byte free, but does not apply if the buffer is filled completely.

This commit switches the conditions so that the interned strings buffer size must be smaller than a quarter of the total OPcache size for the warning to be shown. That the buffer must be either filled completely or by more than 90% remains untouched.

Signed-off-by: MichaIng <micha@dietpi.com>