Fix normalization error when condition’s minimum/maximum are missing in designspace, update test too

Fixes #1346

Lib/fontTools/varLib/__init__.py

@@ -587,8 +587,14 @@ def _add_GSUB_feature_variations(font, axes, internal_axis_supports, rules):
 			space = {}
 			for condition in conditions:
 				axis_name = condition["name"]
+				if condition["minimum"]:
 					minimum = normalize(axis_name, condition["minimum"])
+				else:
+					minimum = -1.0
+				if condition["maximum"]:
 					maximum = normalize(axis_name, condition["maximum"])
+				else:
+					maximum = 1.0
 				tag = axis_tags[axis_name]
 				space[tag] = (minimum, maximum)
 			region.append(space)

Tests/varLib/data/FeatureVars.designspace

@@ -9,7 +9,7 @@
     <rules>
         <rule name="dollar-stroke">
             <conditionset>
-                <condition name="weight" minimum="500" maximum="1000" />
+                <condition name="weight" minimum="500" /> <!-- intentionally omitted maximum -->
             </conditionset>
             <sub name="uni0024" with="uni0024.nostroke" />
         </rule>