Fixed numerous warnings from the new cppcheck 1.81

Specifically:

very strange braces!
syntaxError,Common/DataModel/vtkHyperTreeGrid.cxx:699,error,syntax error

changed size()>0 to !empty()
stlSize,Filters/General/vtkLoopBooleanPolyDataFilter.cxx:1426,performance,Possible inefficient checking for 'nocellregion' emptiness.

This useless flag has been there since code was added in 2000 in f50b0909
knownConditionTrueFalse,Common/DataModel/vtkPointLocator.cxx:323,style,Condition 'flag' is always true
knownConditionTrueFalse,Common/DataModel/vtkPointLocator.cxx:415,style,Condition 'flag' is always true
knownConditionTrueFalse,Common/DataModel/vtkStaticPointLocator.cxx:788,style,Condition 'flag' is always true
knownConditionTrueFalse,Common/DataModel/vtkStaticPointLocator.cxx:879,style,Condition 'flag' is always true

This useless 'result' has been there since code was added in 2003 in dd39b9e4
knownConditionTrueFalse,IO/XML/vtkXMLRectilinearGridReader.cxx:236,style,Condition 'result' is always true
knownConditionTrueFalse,IO/XML/vtkXMLRectilinearGridReader.cxx:245,style,Condition 'result' is always true
knownConditionTrueFalse,IO/XML/vtkXMLRectilinearGridReader.cxx:254,style,Condition 'result' is always true

New check in cppcheck 1.81, block is indeed dead code:
oppositeInnerCondition,Rendering/OpenGL/vtkXOpenGLRenderWindow.cxx:272,warning,Opposite inner 'if' condition leads to a dead code block.
oppositeInnerCondition,Rendering/OpenGL/vtkXOpenGLRenderWindow.cxx:293,warning,Opposite inner 'if' condition leads to a dead code block.
oppositeInnerCondition,Rendering/OpenGL/vtkXOpenGLRenderWindow.cxx:349,warning,Opposite inner 'if' condition leads to a dead code block.

false positive, suppressed with zero initialization:
uninitvar,Filters/Statistics/vtkKMeansStatistics.cxx:810,error,Uninitialized variable: curDistance
uninitvar,Filters/Statistics/vtkKMeansStatistics.cxx:812,error,Uninitialized variable: curDistance

free(NULL) is allowed, so just remove null check
knownConditionTrueFalse,IO/Geometry/Testing/Cxx/TestIncrementalOctreePointLocator.cxx:920,style,Condition 'truthIds' is always false
knownConditionTrueFalse,IO/Geometry/Testing/Cxx/TestIncrementalOctreePointLocator.cxx:956,style,Condition 'diskFile' is always false

Simplified the calculation, verified same codegen on x86_64 with godbolt
shiftTooManyBitsSigned,Rendering/Volume/vtkHAVSVolumeMapper.cxx:53,error,Shifting signed 32-bit value by 31 bits is undefined behaviour

These have all been thus since their inception, but a global search find the same pattern in TestDijkstraGraphGeodesicPath.cxx, from which I copied the apparent solution
knownConditionTrueFalse,Interaction/Widgets/Testing/Cxx/TestPolygonalRepresentationHandleWidget.cxx:119,style,Condition 'distanceOffsetSpecified' is always false
knownConditionTrueFalse,Interaction/Widgets/Testing/Cxx/TestPolygonalRepresentationHandleWidget.cxx:199,style,Condition 'distanceOffsetSpecified' is always false
knownConditionTrueFalse,Interaction/Widgets/Testing/Cxx/TestPolygonalSurfaceConstrainedDistanceWidget.cxx:244,style,Condition 'distanceOffsetSpecified' is always false
knownConditionTrueFalse,Interaction/Widgets/Testing/Cxx/TestPolygonalSurfaceConstrainedDistanceWidget.cxx:325,style,Condition 'distanceOffsetSpecified' is always false
knownConditionTrueFalse,Interaction/Widgets/Testing/Cxx/TestSurfaceConstrainedHandleWidget.cxx:117,style,Condition 'distanceOffsetSpecified' is always false
knownConditionTrueFalse,Interaction/Widgets/Testing/Cxx/TestSurfaceConstrainedHandleWidget.cxx:189,style,Condition 'distanceOffsetSpecified' is always false

Toggle with #if instead
knownConditionTrueFalse,Imaging/Hybrid/vtkSurfaceReconstructionFilter.cxx:300,style,Condition 'orientationPropagation' is always true

Added parens
clarifyCalculation,Common/DataModel/vtkLagrangeWedge.cxx:906,style,Clarify calculation precedence for '/' and '?'.