gir: Don't crash on unlabled elements

Without this a class member of

     <field name="xwayland_atoms" introspectable="0">
        <array zero-terminated="0">
          <type c:type="xcb_atom_t"/>
        </array>
     </field>

crashes like

  gi-docgen.py generate --quiet --add-include-path=... --config=doc/foo.toml --output-dir=doc/foo-0 --no-namespace-dir --content-dir=/tmp/doc src/Foo-0.gir
  Traceback (most recent call last):
    File "/tmp/foo/subprojects/gi-docgen/gidocgen/gidocmain.py", line 74, in run
      res = options.run_func(options)
    File "/tmp/foo/subprojects/gi-docgen/gidocgen/gdgenerate.py", line 2827, in run
      parser.parse(options.infile)
    File "/tmp/foo/subprojects/gi-docgen/gidocgen/gir/parser.py", line 85, in parse
      repository = self._parse_tree(tree.getroot())
    File "/tmp/foo/subprojects/gi-docgen/gidocgen/gir/parser.py", line 248, in _parse_tree
      parser_method(node, repository, namespace)
    File "/tmp/foo/subprojects/gi-docgen/gidocgen/gir/parser.py", line 790, in _parse_class
      fields.append(self._parse_field(child))
    File "/tmp/foo/subprojects/gi-docgen/gidocgen/gir/parser.py", line 752, in _parse_field
      ctype = self._parse_ctype(node)
    File "/subprojects/gi-docgen/gidocgen/gir/parser.py", line 344, in _parse_ctype
      target = self._lookup_type(name=tname, ctype=ttype)
    File "/tmp/foo/subprojects/gi-docgen/gidocgen/gir/parser.py", line 131, in _lookup_type
      elif '.' in name:
  TypeError: argument of type 'NoneType' is not iterable

due to the lack of a typename.
3 jobs for unlabled-array-type in 2 minutes and 24 seconds (queued for 5 seconds)
Status Name Job ID Coverage
  Check
passed flake8 #1446631

00:01:30

failed mypy #1446632
allowed to fail

00:01:26

passed reuse #1446633

00:02:23

 
Name Stage Failure
failed
mypy Check
gidocgen/gir/parser.py:984: error: Argument "get_type" to "GType" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:1006: error: Argument "name" to "Union" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:1006: error: Argument "symbol_prefix" to "Union" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:1006: error: Argument "ctype" to "Union" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:1008: error: Argument 1 to "set_version" of "GIRElement" has incompatible type "Optional[str]"; expected "str"
gidocgen/utils.py:809: error: Need type annotation for 'found_programs' (hint: "found_programs: Dict[<type>, <type>] = ...")
Found 204 errors in 3 files (checked 17 source files)
Cleaning up file based variables
ERROR: Job failed: exit code 1