Add extra check for line-style parsing

Fixes #385.

gaphor/core/styling/declarations.py

@@ -164,7 +164,7 @@ def parse_enum(prop, value):
 def parse_line_style(prop, value) -> float:
     if value == "sloppy":
         return 0.5
-    elif isinstance(value, tuple):
+    elif isinstance(value, tuple) and len(value) == 2:
         style, factor = value
         if style == "sloppy":
             if not isinstance(factor, number):

gaphor/core/styling/tests/test_css.py

@@ -207,3 +207,13 @@ def test_line_style(css_value, result):
     props = compiled_style_sheet.match(Node("mytype"))
 
     assert props.get("line-style") == result
+
+
+def test_broken_line_style():
+    # diagram css is missing the closing bracket
+    css = "diagram { line-style: sloppy * { }"
+
+    compiled_style_sheet = CompiledStyleSheet(css)
+
+    props = compiled_style_sheet.match(Node("mytype"))
+    assert props.get("line-style") is None