valgrind reports errors in BestEncInfoCache::isValid

[fbossen]

With commit 69d571b, valgrind typically reports errors in BestEncInfoCache::isValid such as

==1286== Conditional jump or move depends on uninitialised value(s)
==1286== at 0x1001BB86A: BestEncInfoCache::isValid(CodingStructure const&, Partitioner const&, int) (in bin/umake/clang-10.0/x86_64/release/EncoderApp)
==1286== by 0x1001BD92B: EncModeCtrlMTnoRQT::initCULevel(Partitioner&, CodingStructure const&) (in bin/umake/clang-10.0/x86_64/release/EncoderApp)
==1286== by 0x100183BD0: EncCu::xCompressCU(CodingStructure*&, CodingStructure*&, Partitioner&, LutMotionCand*&, LutMotionCand*&) (in bin/umake/clang-10.0/x86_64/release/EncoderApp)
==1286== by 0x100182FDA: EncCu::compressCtu(CodingStructure&, UnitArea const&, unsigned int, int const*, int const*) (in bin/umake/clang-10.0/x86_64/release/EncoderApp)
==1286== by 0x1001DB566: EncSlice::encodeCtus(Picture*, bool, bool, unsigned int, unsigned int, EncLib*) (in bin/umake/clang-10.0/x86_64/release/EncoderApp)
==1286== by 0x1001DA27C: EncSlice::compressSlice(Picture*, bool, bool) (in bin/umake/clang-10.0/x86_64/release/EncoderApp)
==1286== by 0x1001A0123: EncGOP::compressGOP(int, int, std::1::list<Picture*, std::1::allocator<Picture*> >&, std::1::list<UnitBuf<short>*, std::1::allocator<UnitBuf<short>*> >&, bool, bool, InputColourSpaceConversion, bool, bool) (in bin/umake/clang-10.0/x86_64/release/EncoderApp)
==1286== by 0x1001B3F50: EncLib::encode(bool, PelStorage*, PelStorage*, InputColourSpaceConversion, std::1::list<UnitBuf<short>*, std::1::allocator<UnitBuf<short>*> >&, int&) (in bin/umake/clang-10.0/x86_64/release/EncoderApp)
==1286== by 0x100004048: EncApp::encode() (in bin/umake/clang-10.0/x86_64/release/EncoderApp)
==1286== by 0x100054C8F: main (in bin/umake/clang-10.0/x86_64/release/EncoderApp)

[fbossen]

The following fixes the issue
​https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/merge_requests/234