Don't set un-parseable numbers to 0 in the config

Previously if an integer or float field was empty it would
default to zero instead of undefined which made it inconsistent
with string value fields.

Now the config value is only set as a Number when it can be
parsed as one.

src/app/config-panel.coffee

@@ -22,17 +22,20 @@ class ConfigPanel extends View
             input.attr('checked', value)
           else
             input.val(value) if value
-        input.on 'change', ->
+        input.on 'change', =>
           value = input.val()
-          config.set name, switch type
-            when 'int'
-              parseInt(value)
-            when 'float'
-              parseFloat(value)
-            when 'checkbox'
-              !!input.attr('checked')
-            else
-              value
+          if type == 'checkbox'
+            value = !!input.attr('checked')
+          else
+            value = @parseValue(type, value)
+          config.set(name, value)
+
+  parseValue: (type, value) ->
+    switch type
+      when 'int' then value = parseInt(value) or value
+      when 'float' then value = parseFloat(value) or value
+    value = undefined if value == ''
+    value
 
   bindEditors: ->
     for editor in @find('.editor[id]').views()
@@ -45,9 +48,5 @@ class ConfigPanel extends View
           value ?= ""
           editor.setText(value.toString())
 
-        editor.getBuffer().on 'contents-modified', ->
-          value = editor.getText()
-          if type == 'int' then value = parseInt(value) or 0
-          if type == 'float' then value = parseFloat(value) or 0
-          if value == "" then value = undefined
-          config.set name, value
+        editor.getBuffer().on 'contents-modified', =>
+          config.set(name, @parseValue(type, editor.getText()))