Fix two random test failures in graphs

[kliem]

Part of #32544:

sage -t --long --random-seed=180924489930967511277954046005685261728 src/sage/graphs/base/sparse_graph.pyx
**********************************************************************
File "src/sage/graphs/base/sparse_graph.pyx", line 1163, in sage.graphs.base.sparse_graph._test_adjacency_sequence_out
Failed example:
    _test_adjacency_sequence_out()  # long time
Exception raised:
    Traceback (most recent call last):
      File "/home/jonathan/Applications/sage/local/lib/python3.8/site-packages/sage/doctest/forker.py", line 694, in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/home/jonathan/Applications/sage/local/lib/python3.8/site-packages/sage/doctest/forker.py", line 1088, in compile_and_execute
        exec(compiled, globs)
      File "<doctest sage.graphs.base.sparse_graph._test_adjacency_sequence_out[1]>", line 1, in <module>
        _test_adjacency_sequence_out()  # long time
      File "sage/graphs/base/sparse_graph.pyx", line 1189, in sage.graphs.base.sparse_graph._test_adjacency_sequence_out (build/cythonized/sage/graphs/base/sparse_graph.c:9302)
        u = randint(low, n - 1)
      File "/home/jonathan/Applications/sage/local/lib/python3.8/site-packages/sage/misc/prandom.py", line 137, in randint
        return _pyrand().randint(a, b)
      File "/home/jonathan/Applications/sage/local/lib/python3.8/site-packages/sage/cpython/_py2_random.py", line 220, in randint
        return self.randrange(a, b+1)
      File "/home/jonathan/Applications/sage/local/lib/python3.8/site-packages/sage/cpython/_py2_random.py", line 195, in randrange
        raise ValueError("empty range for randrange() (%d,%d, %d)" %
    ValueError: empty range for randrange() (0,0, 0)

sage -t --long --random-seed=180924489930967511277954046005685261728 src/sage/graphs/generators/families.py
**********************************************************************
File "src/sage/graphs/generators/families.py", line 1477, in sage.graphs.generators.families.FriendshipGraph
Failed example:
    G.diameter()
Expected:
    2
Got:
    1

CC: @dcoudert

Component: graph theory

Keywords: fuzzing

Author: Jonathan Kliem

Branch/Commit: 50e4c8d

Reviewer: David Coudert

Issue created by migration from https://trac.sagemath.org/ticket/32772

[kliem]

Branch: public/32772

[kliem]

Commit: 50e4c8d

[kliem]

New commits:

50e4c8d

fix two test failures for graphs

[kliem]

Author: Jonathan Kliem

[dcoudert]

Reviewer: David Coudert

[dcoudert]

comment:2

I agree with your changes.

[kliem]

comment:3

Thank you.

[vbraun]

Changed branch from public/32772 to 50e4c8d