Bug #16737: Change BlockSize type to prevent overflow

Changing BlockSize type from unsigned int to int is acceptable  since
the value computed for this->BlockSize in the class is known to never
be anything but an int(see vtkwindBladeReader::FindVariableOffsets)

IO/Geometry/vtkWindBladeReader.h

@@ -138,7 +138,7 @@ protected:
   int* VariableBasicType;  // FLOAT or INTEGER
   int* VariableByteCount;  // Number of bytes in basic type
   long int* VariableOffset;  // Offset into data file
-  unsigned int BlockSize;   // Size of every data block
+  int BlockSize;   // Size of every data block
   int GBlockSize;  // Size of every data block
 
   vtkFloatArray** Data;   // Actual data arrays