Fix lincomb

[SoongNoonien]

julia> T = genchartab("SL3.n1");

julia> lincomb([1,1], [T[2], T[6]])
Generic character of SL3.n1
  with parameters 
    nl2 ∈ {1,…, q - 1}, ml2 ∈ {1,…, q - 1} except -ml2 + nl2 ∈ (q - 1)ℤ
  of degree q^3 + 3*q^2 + 3*q + 1
  with values
    q^3 + 3*q^2 + 3*q + 1
    3*q + 1
    1
    (q + 1)*exp(2π𝑖((a*ml2 + a*nl2)//(q - 1))) + (q + 1)*exp(2π𝑖((a*ml2 - 2*a*nl2)//(q - 1))) + q + 1 + (q + 1)*exp(2π𝑖((-2*a*ml2 + a*nl2)//(q - 1)))
    exp(2π𝑖((a*ml2 + a*nl2)//(q - 1))) + exp(2π𝑖((a*ml2 - 2*a*nl2)//(q - 1))) + 1 + exp(2π𝑖((-2*a*ml2 + a*nl2)//(q - 1)))
    exp(2π𝑖((-a*nl2 + b*ml2 - b*nl2)//(q - 1))) + exp(2π𝑖((-a*ml2 + a*nl2 - b*ml2)//(q - 1))) + exp(2π𝑖((a*ml2 + b*nl2)//(q - 1))) + exp(2π𝑖((-a*ml2 - b*ml2 + b*nl2)//(q - 1))) + exp(2π𝑖((a*ml2 - a*nl2 - b*nl2)//(q - 1))) + 2 + exp(2π𝑖((a*nl2 + b*ml
    2)//(q - 1)))
    0
    -1

julia> lincomb([1,2,2],[T[1],T[2],T[3]])
Generic character of SL3.n1
  of degree 2*q^3 + 2*q^2 + 2*q + 1
  with values
    2*q^3 + 2*q^2 + 2*q + 1
    2*q + 1
    1
    4*q + 3
    3
    7
    -1
    1

Fixes: #189

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 90.98%. Comparing base (7c5d868) to head (77a7093).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Shifts.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #192      +/-   ##
==========================================
- Coverage   91.20%   90.98%   -0.22%     
==========================================
  Files          13       13              
  Lines         841      843       +2     
==========================================
  Hits          767      767              
- Misses         74       76       +2     

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