[imap] Gracefully handle bodystructure where boundaries are reported …

…as NIL.

Some servers (e.g mail.ru) report boundaries as NIL for multipart messages.
from my understanding of RFC2046 this is invalid, but we can gracefully handle
those by setting them to empty.
Avoids crash when requesting a partAt() for a message that does not exist,
this happened due to NIL boundaries, but no need to crash in such cases.

qmf/src/libraries/qmfclient/qmailmessage.cpp

@@ -3948,8 +3948,13 @@ const QMailMessagePart& QMailMessagePartContainerPrivate::partAt(const QMailMess
     const QList<QMailMessagePart>* partList = &_messageParts; 
 
     foreach (uint index, location.d->_indices) {
-        part = &(partList->at(index - 1));
-        partList = &(part->impl<const QMailMessagePartContainerPrivate>()->_messageParts);
+        if (index >= 0 && index <= partList->size()) {
+            part = &(partList->at(index - 1));
+            partList = &(part->impl<const QMailMessagePartContainerPrivate>()->_messageParts);
+        } else {
+            qMailLog(Messaging) << Q_FUNC_INFO << "Invalid index, container does not have a part at " << index;
+            Q_ASSERT(false);
+        }
     }
 
     Q_ASSERT(part);
@@ -3962,8 +3967,13 @@ QMailMessagePart& QMailMessagePartContainerPrivate::partAt(const QMailMessagePar
     QList<QMailMessagePart>* partList = &_messageParts; 
 
     foreach (uint index, location.d->_indices) {
-        part = &((*partList)[index - 1]);
-        partList = &(part->impl<QMailMessagePartContainerPrivate>()->_messageParts);
+        if (index >= 0 && index <= partList->size()) {
+            part = &((*partList)[index - 1]);
+            partList = &(part->impl<QMailMessagePartContainerPrivate>()->_messageParts);
+        } else {
+            qMailLog(Messaging) << Q_FUNC_INFO << "Invalid index, container does not have a part at " << index;
+            Q_ASSERT(false);
+        }
     }
 
     return *part;

qmf/src/plugins/messageservices/imap/imapstructure.cpp

@@ -435,7 +435,12 @@ void setMultipartFromDescription(const QStringList &structure, QMailMessagePartC
         }
         for ( ; (it != end) && ((it + 1) != end); it += 2) {
             if ((*it).trimmed().toUpper() == "BOUNDARY") {
-                container->setBoundary((*(it + 1)).toLatin1());
+                const QString boundary((*(it + 1)));
+                if (boundary.toUpper() == "NIL") {
+                    container->setBoundary(QByteArray());
+                } else {
+                    container->setBoundary(boundary.toLatin1());
+                }
             }
         }
     }