knockdown: mitre limit cannot be zero (#3537)

lib/extensions/knockdown_fill.py

@@ -66,7 +66,7 @@ class KnockdownFill(InkstitchExtension):
             self.options.offset * PIXELS_PER_MM,
             cap_style=int(self.options.join_style),
             join_style=int(self.options.join_style),
-            mitre_limit=int(self.options.mitre_limit)
+            mitre_limit=float(max(self.options.mitre_limit, 0.1))
         )
         combined_shape = combined_shape.simplify(0.3)
         combined_shape = ensure_multi_polygon(combined_shape)

templates/knockdown_fill.xml

@@ -16,13 +16,13 @@
     <param name="notebook" type="notebook">
       <page name="options" gui-text="Options">
         <param name="keep-holes" type="bool" gui-text="Keep holes">true</param>
-        <param name="offset" type="float" gui-text="Offset">1</param>
+        <param name="offset" type="float" gui-text="Offset" min="0" max="50">1</param>
         <param name="join-style" type="optiongroup" gui-text="Method">
            <option value="1">Round</option>
            <option value="2">Mitre</option>
            <option value="3">Bevel</option>
         </param>
-        <param name="mitre-limit" type="float" gui-text="Mitre limit">5.0</param>
+        <param name="mitre-limit" type="float" gui-text="Mitre limit" min="0.1" max="50">5.0</param>
       </page>
       <page name="info" gui-text="Help">
         <label appearance="header">This extension generates a knockdown fill area with a specified offset around selected elements.</label>