gradient mesh deselects after new node added

[Pétery Tamás]

Another problem with the mesh tool.

Once you double click and finally add new nodes, the whole mesh gets deselected by a sudden while the mesh tool is still active.

Even worse when you can't add new nodes by double clicking it still deselects the mesh.

To top that, sometimes when you double click on the object once it has a mesh already, it replaces it with a completely new one.

Tested on win 10 64bit Inkscape 0.92pre3 15195.

[su_v (suv-lp)]

Testing with RC builds (on OS X 10.7.5):
- reproduced with Inkscape 0.92pre3
- not reproduced with Inkscape 0.92pre4

Fixed for stable branch 0.92.x in r15216:
https://bazaar.launchpad.net/~inkscape.dev/inkscape/0.92.x/revision/15216

Note: with Inkscape 0.92pre3 you can use the workaround described here:
http://wiki.inkscape.org/wiki/index.php/Mesh_Gradients_Bugs#Inserting_row.2Fcolumn_with_double_click:_Fixed
(use 'Ctrl+Doubleclick' to insert rows/columns without selected nodes and to avoid deselection of the meshgradient itself)