fix bug around wrong number of vertices

Change-Id: I52c6c0b5d815266a254a75eabfe8947ccc44bfb5

vcl/opengl/gdiimpl.cxx

@@ -307,7 +307,7 @@ void OpenGLSalGraphicsImpl::DrawConvexPolygon( sal_uInt32 nPoints, const SalPoin
     }
 
     glEnableVertexAttribArray( GL_ATTRIB_POS );
-    glVertexAttribPointer( GL_ATTRIB_POS, 2, GL_FLOAT, GL_FALSE, 0, &aVertices[0] );
+    glVertexAttribPointer( GL_ATTRIB_POS, nPoints * 2, GL_FLOAT, GL_FALSE, 0, &aVertices[0] );
     glDrawArrays( GL_TRIANGLE_FAN, 0, nPoints );
     glDisableVertexAttribArray( GL_ATTRIB_POS );
 }