feat(xmlwf): add -a and -b arg non-completions

$ xmlwf -v
xmlwf using expat_2.4.1
[...]
$ xmlwf --help
[...]
  -a FACTOR     set maximum tolerated [a]mplification factor [...]
  -b BYTES      set number of output [b]ytes needed to activate [...]
[...]

Bundle a non-arg option in related test to test bundling behavior while
at it.

Author: scop

completions/xmlwf

@@ -15,7 +15,7 @@ _xmlwf()
                 -- "$cur"))
             return
             ;;
-        -*v)
+        -*[abv])
             return
             ;;
     esac

test/t/test_xmlwf.py

@@ -9,3 +9,7 @@ def test_1(self, completion):
     @pytest.mark.complete("xmlwf -", require_cmd=True)
     def test_2(self, completion):
         assert completion
+
+    @pytest.mark.complete("xmlwf -sa ")
+    def test_no_arg_to_a(self, completion):
+        assert not completion