Check for unsafe drop

[jeremypw]

Fixes #793

In order to use the same code to check for unsafe input, both paste and drop end up feeding the text to the terminal child. This actually saves some lines.

[teamcons]

The issue was marked critical, but the PR seems out of date - Any ETA for merging ?

[jeremypw]

I marked it critical because the issue has theoretical security implications, but its not a new issue. I guess folks are focused on getting OS8 released atm.

[ryonakano]

The clipboard or dragged text are no longer pasted if we once uncheck "Show paste protection warnings" in the UnsafePasteDialog.

[jeremypw]

@ryonakano Oops! Thanks for spotting that. Now fixed. It occurred to me that if unsafe paste alert is turned off in the dialog, there is no way of turning it back on through the UI. Am I right? If so that needs fixing but in another PR.

[jeremypw]

I noticed that this PR was pasting the stripped text into the terminal whereas in master, the text was refetched from the clipboard. Now the stripped text is only used for the dialog message as before.

[teamcons]

@ryonakano Oops! Thanks for spotting that. Now fixed. It occurred to me that if unsafe paste alert is turned off in the dialog, there is no way of turning it back on through the UI. Am I right? If so that needs fixing but in another PR.

following your comment i did a PR for that.
Pantheon-tweaks always offered that option, im not sure why there was no toggle-back in first instance.

[ryonakano]

The clipboard or dragged text are no longer pasted if we once uncheck "Show paste protection warnings" in the UnsafePasteDialog.

Confirmed this is fixed, thank you!

Leaving another two tiny comments.

Changes addressed

[ryonakano]

Code looks good and fixes the linked issue. Thank you!