HPCC-31521 Prevent crash in dafilesrv with an invalid filter #8019

Job	Run time
Check Skip	12s
Build Docker (ubuntu-22.04, k8s, true, schedule)	14s
Build Bare Metal (ubuntu-20.04, mono, sudo, -DCMAKE_BUILD_TYPE=RelWithDebInfo -DINCLUDE_PLUGINS=O...	2s
Build Docker (ubuntu-22.04, schedule)	1m 0s
Build Bare Metal (ubuntu-22.04, mono, sudo, -DCMAKE_BUILD_TYPE=RelWithDebInfo -DINCLUDE_PLUGINS=O...	23m 2s
Build Bare Metal (windows-2019, -T host=x64 -A x64 -DUSE_OPTIONAL=OFF -DCLIENTTOOLS_ONLY=ON -DUSE...	2s
Build Docker (ubuntu-20.04, schedule)	12s
Build Docker (centos-8, schedule)	14s
Build Bare Metal (windows-2022, -T host=x64 -A x64 -DUSE_OPTIONAL=OFF -DCLIENTTOOLS_ONLY=ON -DUSE...	14m 46s
Build Bare Metal (macos-11, mono, sudo, -DCMAKE_BUILD_TYPE=Release -DUSE_OPTIONAL=OFF -DCLIENTTOO...	4s
Build Docker (centos-7, pull_request)	42m 10s
Build Bare Metal (macos-12, mono, sudo, -DCMAKE_BUILD_TYPE=Release -DUSE_OPTIONAL=OFF -DCLIENTTOO...	13m 22s
Build Docker (amazonlinux, schedule)	13s
Build Docker (centos-7, LN, true, schedule)	16s
	1h 35m 49s

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