Backport r841594 by tmcguire to the 4.1 branch:

Invalidate the folder when encountering a zero serial number.
I have still no idea why the serial number was zero in the first
place, but at least this fixes the problem that those messages
could not be displayed.

(Marc, sorry, but I re-enabled the debug output here)

CCBUG: 149715


svn path=/branches/KDE/4.1/kdepim/; revision=842189

kmmsgdict.cpp

@@ -467,8 +467,16 @@ int KMMsgDict::readFolderIds( FolderStorage& storage )
       return -1;
     }
 
-    //if (!msn)
-      //kDebug(5006) <<"Dict found zero serial number in folder" << folder->label();
+    // We found a serial number that is zero. This is not allowed, and would
+    // later cause problems like in bug 149715.
+    // Therefore, we invalidate the folder when this happens.
+    if ( msn == 0 ) {
+      kWarning() << "Found serial number zero at index" << index << "in folder" << filename;
+      kWarning() << "Invalidating folder.";
+      fclose( fp );
+      delete rentry;
+      return -1;
+    }
 
     // Insert into the dict. Don't use dict->replace() as we _know_
     // there is no entry with the same msn, we just made sure.
@@ -565,6 +573,9 @@ int KMMsgDict::writeFolderIds( const FolderStorage &storage )
     quint32 msn = rentry->getMsn(index);
     if (!fwrite(&msn, sizeof(msn), 1, fp))
       return -1;
+    if ( msn == 0 ) {
+      kWarning() << "Serial number of message at index" << index << "is zero in folder" << storage.label();
+    }
   }
 
   rentry->sync();