file location not stored when opening/saving materials

[uwestoehr]

Word size of FreeCAD: 64-bit, Version: 0.18.15780 (Git)
Build type: Release
Branch: master
Hash: f94e76c1116ec3b818961ff65131b3d86fa5b95e
Python version: 2.7.14
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.2.0

To reproduce:

- add a material, then "use FreeCAD material editor"
- press Open
- select e.g. a FCMat file in this folder "D:\test\FreeCAD"
- now you might notice that you loaded the wrong file and thus press Open again

result: the default file location is not the last used "D:\test\FreeCAD" but the folder of the freecad.exe.

[uwestoehr]

To avoid that his issue will be forgotten, I created issue #3825.

[bernd]

git commit a73b10203