[DBMail 0001070]: dbmail-export segfaults on one user, user has messages but cannot retrieve them via imapd or pop3d

A NOTE has been added to this issue. 
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http://www.dbmail.org/mantis/view.php?id=1070 
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Reported By:                faxguy
Assigned To:                
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Project:                    DBMail
Issue ID:                   1070
Category:                   Command-Line programs (dbmail-users, dbmail-util)
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
target:                      
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Date Submitted:             23-Mar-15 17:02 CET
Last Modified:              23-Mar-15 17:05 CET
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Summary:                    dbmail-export segfaults on one user, user has
messages but cannot retrieve them via imapd or pop3d
Description: 
After months of proper operations, suddenly one user account was unable to
retrieve any messages due to a corruption with one message.  However, all
other user accounts were behaving normally.

dbmail-export segfaulted when attempting to export the messages for that
user account.

dbmail-util did not repair or remove the corrupted message.

I will be attaching an strace of the dbmail-export segfault and also a
patch to fix that segfault.
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 (0003696) faxguy (reporter) - 23-Mar-15 17:05
 http://www.dbmail.org/mantis/view.php?id=1070#c3696 
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The dbmail-export segfault is fixed by the attached patch.
dbmail_message_retrieve() can return NULL, and this condition was not being
handled.

I note that a NULL return from dbmail_message_retrieve() is also not
handled in both src/dm_http.c and src/maintenance.c, but I did not address
these since my immediate use would not have allowed me to test any code
changes to there.  I will leave that to you.

I would like to see dbmail-util correct or remove the corrupt message.  I
would much-prefer to just run dbmail-util than to run hard-code a printf
into dbmail-export and then delete a record from the database. 

Issue History 
Date Modified    Username       Field                    Change               
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23-Mar-15 17:02  faxguy         New Issue                                    
23-Mar-15 17:03  faxguy         File Added: strace.txt                       
23-Mar-15 17:04  faxguy         File Added: dbmail-nullmessagefix.patch         
          
23-Mar-15 17:05  faxguy         Note Added: 0003696                          
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