HPCC-10779 Caching nohits will interfere with dynamic files

Fix a regression in 4.4.4-rc8

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #5341 from richardkchapman/roxie-write-cache

HPCC-10779 Caching nohits will interfere with dynamic files

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>