-Werror,-Wself-assign

...ever since 2bd76c39 "INTEGRATION: CWS aw033",
and looks like it wants to use the

  aRetval = rCandidate.getB2DPoint(nIndex);

already assigned to it ahead of the if/else branches.

Change-Id: Iac242281312fe28b9a17a6a2a930e9597f77b7aa
Reviewed-on: https://gerrit.libreoffice.org/52811Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
(cherry picked from commit 4bf1bf9d)

basegfx/source/polygon/b2dpolygontools.cxx

@@ -625,7 +625,6 @@ namespace basegfx
                     else if(fTools::equalZero(fDistance))
                     {
                         // start point of chosen edge
-                        aRetval = aRetval;
                     }
                     else
                     {