export fails with related record location-type fields when contact has no such relationships

to reproduce:

• search for contacts and select one that does not have an employer relationship (it applies to all rel types)
• select export from the action dropdown
• choose to select your fields
• choose: employee of > phone > home > phone
• choose: employee of > phone > home > fax
• export

the export errors with: DB Error: value count on row

this is because the header row is constructed correctly, but the insertion into the temp table has less data values than columns, and thus fails.

the issue is that if the exported contact does not have the relationship in question, the code to construct those values in the $rows array is skipped, and consequently we have too few data columns for the headers.

the bug entered in 4.1 with this commit:
https://fisheye2.atlassian.com/browse/CiviCRM/trunk/CRM/Export/BAO/Export.php?r2=37838&r1=37831

which was part of this issue:
http://issues.civicrm.org/jira/browse/CRM-9295

by adding the condition that we have a valid relationship object, it skips records for which no such relationship exists, and breaks the export.

i've reverted that commit and am not seeing any issues with the household merging (which was the jira issue topic). maybe Deepak can review and recall what prompted the patch.