Export Watch only missing .dat file extension

[polespinasa]

When exporting a watchonly wallet using the GUI the .dat extension is not automatically added to the file.
The GUI then is not able to restore a wallet without the explicit .dat extension.

Note: I did not check if this also happens using RPC, will update the issue when tested.
Edit: The RPC is unaffected by this, it does allow non .dat files.

With .dat works:

Without .dat does not see it:

[polespinasa]

This is fixed in #957

[hebasto]

When exporting a watchonly wallet using the GUI the .dat extension is not automatically added to the file.

The GUI behaviour is consistent with the RPC.

The GUI then is not able to restore a wallet without the explicit .dat extension.

Perhaps we could provide the user with a hint?