Fix class AbstractBitMap64

Author: chdemko

pyroaring/abstract_bitmap.pxi

@@ -1334,6 +1334,7 @@ cdef class AbstractBitMap64:
             return bitmaps[0] - bitmaps[1]
         else:
             result = BitMap64(bitmaps[0])
+            result._h_val = 0
             for bm in bitmaps[1:]:
                 result -= bm
             return bitmaps[0].__class__(result)
@@ -1384,6 +1385,7 @@ cdef class AbstractBitMap64:
             return bitmaps[0] & bitmaps[1]
         else:
             result = BitMap64(bitmaps[0])
+            result._h_val = 0
             for bm in bitmaps[1:]:
                 result &= bm
             return bitmaps[0].__class__(result)