Incorrect results with partially out-of-bounds part select

OPEN: last verified in Verilator 3_906

This should return y=4'b100x for a=1, but verilator returns y=0 instead (the MSB should be '1', obviously we don't care about the 'x' in the LSB that is the result of the (by one bit) out-of-bounds part select):

module issue_057(a, y);
  input [2:0] a;
  output [3:0] y;
  localparam [5:15] p = 51681708;
  assign y = p[15 + a -: 5];

Self-contained test case: test020.v, test020_tb.v,,

This is with git e8edbad (verilator_3_864).

2014-09-23 Reported as Issue #823
2017-07-01 Still broken in Verilator GIT 1da5a33 (3_906)

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