Issue #2786735 by recrit, eiriksm, ranjith_kumar_k_u, immaculatexavier,...

Issue #2786735 by recrit, eiriksm, ranjith_kumar_k_u, immaculatexavier, ravi.shankar, zaporylie, smustgrave, TrevorBradley, johnle, GaëlG, jefuri, alexpott, poker10: Image derivative generation does not work if effect "Convert" in use and file stored in private filesystem

(cherry picked from commit 31f9e8a9)