Show explicit error message for SSSP run over a graph with no edge weight

[doudoubobo]

Fixes #1878

[codecov-commenter]

Codecov Report

Merging #2929 (9a43220) into main (34b3650) will decrease coverage by 7.76%.
The diff coverage is 71.42%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2929      +/-   ##
==========================================
- Coverage   73.96%   66.21%   -7.76%     
==========================================
  Files          99       99              
  Lines       10672    10668       -4     
==========================================
- Hits         7894     7064     -830     
- Misses       2778     3604     +826     

Impacted Files	Coverage Δ
python/graphscope/analytical/app/sssp.py	86.66% <71.42%> (-13.34%)	⬇️

... and 19 files with indirect coverage changes

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