Build failures with GCC 12 and -Werror

[jrmuizel]

The mingw CI build is now broken because it has updated to GCC 12

In function 'void AnchorPredInter16x8Mv(int16_t (*)[30][2], int8_t (*)[30], int32_t, int8_t, int16_t*)',
    inlined from 'virtual void PredMvTest_PredInter16x8Mv_Test::TestBody()' at ../test/decoder/DecUT_PredMv.cpp:238:27:
../test/decoder/DecUT_PredMv.cpp:103:18: error: 'sAncMvPred' may be used uninitialized [-Werror=maybe-uninitialized]
  103 |     const int8_t kiTopRef = iRefIndex[0][1];
      |                  ^~~~~~~~
../test/decoder/DecUT_PredMv.cpp: In member function 'virtual void PredMvTest_PredInter16x8Mv_Test::TestBody()':
../test/decoder/DecUT_PredMv.cpp:228:17: note: 'sAncMvPred' declared here
  228 |   SAnchorMvPred sAncMvPred;
      |                 ^~~~~~~~~~
In function 'void AnchorPredInter16x8Mv(int16_t (*)[30][2], int8_t (*)[30], int32_t, int8_t, int16_t*)',
    inlined from 'virtual void PredMvTest_PredInter16x8Mv_Test::TestBody()' at ../test/decoder/DecUT_PredMv.cpp:238:27:
../test/decoder/DecUT_PredMv.cpp:109:18: error: 'sAncMvPred' may be used uninitialized [-Werror=maybe-uninitialized]
  109 |     const int8_t kiLeftRef = iRefIndex[0][18];
      |                  ^~~~~~~~~
../test/decoder/DecUT_PredMv.cpp: In member function 'virtual void PredMvTest_PredInter16x8Mv_Test::TestBody()':
../test/decoder/DecUT_PredMv.cpp:228:17: note: 'sAncMvPred' declared here
  228 |   SAnchorMvPred sAncMvPred;
      |                 ^~~~~~~~~~
In function 'void AnchorPredInter8x16Mv(int16_t (*)[30][2], int8_t (*)[30], int32_t, int8_t, int16_t*)',
    inlined from 'virtual void PredMvTest_PredInter8x16Mv_Test::TestBody()' at ../test/decoder/DecUT_PredMv.cpp:257:27:
../test/decoder/DecUT_PredMv.cpp:79:18: error: 'sAncMvPred' may be used uninitialized [-Werror=maybe-uninitialized]
   79 |     const int8_t kiLeftRef = iRefIndex[0][6];
      |                  ^~~~~~~~~
../test/decoder/DecUT_PredMv.cpp: In member function 'virtual void PredMvTest_PredInter8x16Mv_Test::TestBody()':
../test/decoder/DecUT_PredMv.cpp:247:17: note: 'sAncMvPred' declared here
  247 |   SAnchorMvPred sAncMvPred;
      |                 ^~~~~~~~~~
In function 'void AnchorPredInter8x16Mv(int16_t (*)[30][2], int8_t (*)[30], int32_t, int8_t, int16_t*)',
    inlined from 'virtual void PredMvTest_PredInter8x16Mv_Test::TestBody()' at ../test/decoder/DecUT_PredMv.cpp:257:27:
../test/decoder/DecUT_PredMv.cpp:85:12: error: 'sAncMvPred' may be used uninitialized [-Werror=maybe-uninitialized]
   85 |     int8_t iDiagonalRef = iRefIndex[0][5]; //top-right
      |            ^~~~~~~~~~~~
../test/decoder/DecUT_PredMv.cpp: In member function 'virtual void PredMvTest_PredInter8x16Mv_Test::TestBody()':
../test/decoder/DecUT_PredMv.cpp:247:17: note: 'sAncMvPred' declared here
  247 |   SAnchorMvPred sAncMvPred;
      |                 ^~~~~~~~~~
In function 'void AnchorPredInter8x16Mv(int16_t (*)[30][2], int8_t (*)[30], int32_t, int8_t, int16_t*)',
    inlined from 'virtual void PredMvTest_PredInter8x16Mv_Test::TestBody()' at ../test/decoder/DecUT_PredMv.cpp:257:27:
../test/decoder/DecUT_PredMv.cpp:88:20: error: 'sAncMvPred' may be used uninitialized [-Werror=maybe-uninitialized]
   88 |       iDiagonalRef = iRefIndex[0][2]; //top-left for 8*8 block(index 1)
      |       ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
../test/decoder/DecUT_PredMv.cpp: In member function 'virtual void PredMvTest_PredInter8x16Mv_Test::TestBody()':
../test/decoder/DecUT_PredMv.cpp:247:17: note: 'sAncMvPred' declared here
  247 |   SAnchorMvPred sAncMvPred;
      |                 ^~~~~~~~~~