Default to 80 when editor.preferredLineLength <= 0

Previously any non-null value would be used as the target
column in the wrap guide and autoflow packages when really
80 should have been used if the value was non-postive.

Now config.getPositiveInt() is called with a default value
of 80 if the current value isn't already positive.

src/app/config.coffee

@@ -100,6 +100,24 @@ class Config
     _.valueForKeyPath(@settings, keyPath) ?
       _.valueForKeyPath(@defaultSettings, keyPath)
 
+  # Public: Retrieves the setting for the given key as an integer number.
+  #
+  # keyPath - The {String} name of the key to retrieve
+  # Returns the value from Atom's default settings, the user's configuration file,
+  # or `NaN` if the key doesn't exist in either.
+  getInt: (keyPath, defaultValueWhenFalsy) ->
+    parseInt(@get(keyPath))
+
+  # Public: Retrieves the setting for the given key as a positive integer number.
+  #
+  # keyPath - The {String} name of the key to retrieve
+  # defaultValue - The integer {Number} to fall back to if the value isn't
+  #                positive
+  # Returns the value from Atom's default settings, the user's configuration file,
+  # or `defaultValue` if the key value isn't greater than zero.
+  getPositiveInt: (keyPath, defaultValue) ->
+    Math.max(@getInt(keyPath), 0) or defaultValue
+
   # Public: Sets the value for a configuration setting.
   #
   # This value is stored in Atom's internal configuration file.

src/packages/autoflow/autoflow.coffee

@@ -8,7 +8,7 @@ module.exports =
       editor.getBuffer().change(range, @reflow(editor.getTextInRange(range)))
 
   reflow: (text) ->
-    wrapColumn = config.get('editor.preferredLineLength') ? 80
+    wrapColumn = config.getPositiveInt('editor.preferredLineLength', 80)
     lines = []
 
     currentLine = []

src/packages/wrap-guide/lib/wrap-guide-view.coffee

@@ -19,7 +19,7 @@ class WrapGuideView extends View
     @subscribe $(window), 'resize', => @updateGuide()
 
   getDefaultColumn: ->
-    config.get('editor.preferredLineLength') ? 80
+    config.getPositiveInt('editor.preferredLineLength', 80)
 
   getGuideColumn: (path) ->
     customColumns = config.get('wrapGuide.columns')