[qmf] Correctly handle multipart/signed parts

multipart/signed parts can be the top level part having any other valid
containers inside as per RFC1847.

qmf/src/libraries/qmfclient/qmailmessage.cpp

@@ -1047,6 +1047,9 @@ namespace findBody
         case QMailMessagePart::MultipartNone:
             return inMultipartNone(part, ctx);
 
+        case QMailMessagePart::MultipartMixed:
+            return inMultipartMixed(part, ctx);
+
         case QMailMessagePart::MultipartAlternative:
             return inMultipartAlternative(part, ctx);
 
@@ -1150,9 +1153,12 @@ namespace findAttachments
             if (found) {
                 found->clear();
             }
-            if (container.multipartType() == QMailMessagePart::MultipartMixed)
+            if (container.multipartType() == QMailMessagePart::MultipartMixed) {
                 inMultipartMixed(container, found, hasAttachments);
-
+            }
+            if (container.multipartType() == QMailMessagePart::MultipartSigned) {
+                inMultipartSigned(container, found, hasAttachments);
+            }
             // In any case, the default strategy wins, even if there are no attachments
             return true;
         }
@@ -1208,6 +1214,24 @@ namespace findAttachments
                 }
             }
         }
+
+        void inMultipartSigned(const QMailMessagePartContainer &container,
+                               Locations* found,
+                               bool* hasAttachments) const
+        {
+            for (uint i = 0; i < container.partCount(); i++) {
+                const QMailMessagePart &part = container.partAt(i);
+                switch (part.multipartType()) {
+                case QMailMessagePart::MultipartNone:
+                    inMultipartNone(part, found, hasAttachments);
+                    break;
+                default:
+                    // Default to handling as MultipartMixed
+                    inMultipartMixed(part, found, hasAttachments);
+                    break;
+                }
+            }
+        }
     };
 
     class TnefAttachmentFindStrategy : public AttachmentFindStrategy