7z reading of UINT64 data type is wrong for big values

Brief description

large values with a first byte indicating at least 4 additional bytes shift an integer by at least 32bits thus leading to an overflow and an incorrect value - the value needs to be casted to long before the bitshift!
(see the attached patch)

Details from the 7z documentation

UINT64 means real UINT64 encoded with the following scheme:
  Size of encoding sequence depends from first byte:
  First_Byte  Extra_Bytes        Value
  (binary)   
  0xxxxxxx               : ( xxxxxxx           )
  10xxxxxx    BYTE y[1]  : (  xxxxxx << (8 * 1)) + y
  110xxxxx    BYTE y[2]  : (   xxxxx << (8 * 2)) + y
  ...
  1111110x    BYTE y[6]  : (       x << (8 * 6)) + y
  11111110    BYTE y[7]  :                         y
  11111111    BYTE y[8]  :                         y