Reducing iteration count in t/t_merge_cond_blowup causes unrolling error

[gezalore]

Reducing N to 16 in t/t_merge_cond_blowup.v here:

verilator/test_regress/t/t_merge_cond_blowup.v

Line 13 in 0722f47

localparam int N = 4096;

yields this error:

%Error: t/t_merge_cond_blowup.v:46:9: Loop unrolling took too long; probably this is an infinite loop, or set --unroll-count above 1000000000
   46 |         for (int i = 0 ; i < N ; i = i + 1) begin
      |         ^~~

Surely reducing the iteration count should not cause unrolling to fail, especially given the unrolling limit is set to 1e9.

[gezalore]

Fixed with f9f66d7