Support setting number fields to 0

Previously entering 0 would end up as '0' in the config
value instead of as a numeric value.

spec/app/config-panel-spec.coffee

@@ -39,6 +39,12 @@ describe "ConfigPanel", ->
     panel.floatInput.val('90.2').change()
     expect(config.get('foo.float')).toBe 90.2
 
+    panel.intInput.val('0').change()
+    expect(config.get('foo.int')).toBe 0
+
+    panel.floatInput.val('0').change()
+    expect(config.get('foo.float')).toBe 0
+
     panel.stringInput.val('moo').change()
     expect(config.get('foo.string')).toBe 'moo'
 
@@ -102,6 +108,12 @@ describe "ConfigPanel", ->
     expect(config.get('foo.float')).toBe undefined
     expect(config.get('foo.string')).toBe undefined
 
+    panel.intEditor.setText('0')
+    panel.floatEditor.setText('0')
+    window.advanceClock(10000) # wait for contents-modified to be triggered
+    expect(config.get('foo.int')).toBe 0
+    expect(config.get('foo.float')).toBe 0
+
   it "does not save the config value until it has been changed to a new value", ->
     class TestPanel extends ConfigPanel
       @content: ->

src/app/config-panel.coffee

@@ -32,8 +32,12 @@ class ConfigPanel extends View
 
   parseValue: (type, value) ->
     switch type
-      when 'int' then value = parseInt(value) or value
-      when 'float' then value = parseFloat(value) or value
+      when 'int'
+        intValue = parseInt(value)
+        value = intValue unless isNaN(intValue)
+      when 'float'
+        floatValue = parseFloat(value)
+        value = floatValue unless isNaN(floatValue)
     value = undefined if value == ''
     value