fix error when reporting without submitting a file (in some versions anyway) where tmp_name was set to 'none' so the =='' check didn't work

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1619 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9