'Save a copy' crashes if current new document hasn't been saved yet

[su_v]

Regression in current trunk: inkscape crashes when saving a copy of a new document (independent of whether there have been changes to the current document, or whether it is still an unmodified copy of the default template).

Steps to reproduce:
1) mv ~/.config/inkscape{,-bkp}
2) launch inkscape by itself (without file)
3) draw a rectangle
4) 'File > Save a Copy…' as PDF file

Expected result:
A copy of the current drawing is saved as PDF according to the chosen options and the current session can be continued.

Actual result:
Current trunk builds crash after confirming the PDF export options.

Same crash occurs when saving a copy of an unmodified new file e.g. as 'Inkscape SVG'.
Tested and reproduced with current trunk (r11847) on OS X 10.7.4 and Ubuntu 12.10 (VM).

Based on tests with archived builds (OS X 10.7.4):
- not reproduced with Inkscape 0.48.3.1
- not reproduced with trunk <= 11646
- reproduced with trunk >= 11649

Possibly like bug #1070903 related to the changes in revision 11648:
<http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/11648>

[jazzynico (jazzynico)]

Fixed revision 11848. Almost the same issue as in bug #1070903 indeed.