Fix attachment filename with no extension

NEWS

@@ -1,3 +1,9 @@
+3.1.4 (2016-MM-DD)
+------------------
+
+Bug fixes
+ - [web] fixed crash when an attachment filename has no extension
+
 3.1.3 (2016-06-22)
 ------------------
 

UI/MailPartViewers/UIxMailPartViewer.m

@@ -282,7 +282,7 @@
   if ([filename length])
     // We replace any slash by a dash since Apache won't allow encoded slashes by default.
     // See http://httpd.apache.org/docs/2.2/mod/core.html#allowencodedslashes
-    filename = (NSMutableString *)[filename stringByReplacingString: @"/" withString: @"-"];
+    filename = [NSMutableString stringWithString: [filename stringByReplacingString: @"/" withString: @"-"]];
   else
     [filename appendFormat: @"%@-%@",
 	      [self labelForKey: @"Untitled"],