Issue #16511: Use default IDLE width and height if config param is not valid.

Patch Serhiy Storchaka.
diff --git a/Lib/idlelib/FormatParagraph.py b/Lib/idlelib/FormatParagraph.py
index 6a5f9b5..557d8a9 100644
--- a/Lib/idlelib/FormatParagraph.py
+++ b/Lib/idlelib/FormatParagraph.py
@@ -32,7 +32,8 @@
         self.editwin = None
 
     def format_paragraph_event(self, event):
-        maxformatwidth = int(idleConf.GetOption('main','FormatParagraph','paragraph'))
+        maxformatwidth = int(idleConf.GetOption('main','FormatParagraph',
+                                                'paragraph', type='int'))
         text = self.editwin.text
         first, last = self.editwin.get_selection_indices()
         if first and last: