Fix download of HTML body parts

NEWS

@@ -12,6 +12,7 @@ Bug fixes
  - [web] fixed handling of duplicate recipients (#4597)
  - [web] fixed folder export when XSRF validation is enabled (#4502)
  - [web] don't encode filename extension when exporting folders
+ - [web] fixed download of HTML body parts
  - [core] don't always fetch the sorting columns
  - [eas] strip '<>' from bodyId and when forwarding mails
  - [eas] fix search on for Outlook application (#4605 and #4607)

SoObjects/Mailer/SOGoMailBodyPart.m

@@ -35,6 +35,7 @@
 #import <NGImap4/NGImap4Connection.h>
 #import <NGMail/NGMimeMessage.h>
 #import <NGMime/NGMimeMultipartBody.h>
+#import <NGMime/NGMimeType.h>
 
 #import <SoObjects/SOGo/NSDictionary+Utilities.h>
 #import <SoObjects/SOGo/NSObject+Utilities.h>
@@ -265,10 +266,15 @@ static BOOL debugOn = NO;
   if (!obj)
     {
       /* lookup body part */
-      if ([self isBodyPartKey: _key])
-	obj = [self lookupImap4BodyPartKey: _key inContext: _ctx];
+      if ([self isBodyPartKey: _key]) {
+        obj = [self lookupImap4BodyPartKey: _key inContext: _ctx];
+      }
       else if ([_key isEqualToString: @"asAttachment"])
-	[self setAsAttachment];
+        {
+          // Don't try to render the part; rewrite object to a simple body part.
+          obj = [SOGoMailBodyPart objectWithName: [self nameInContainer] inContainer: [self container]];
+          [obj setAsAttachment];
+        }
       /* should check whether such a filename exist in the attached names */
       if (!obj)
 	obj = self;