[Linux] Be more strict about entering debug mode
[Linux] Be more strict about entering debug mode

Previously, a GUI user could start TBB in debug mode by dragging and
dropping a file onto start-tor-browser.

Found by taylanub (see ticket #3432).

Shondoit/torbrowser,Shondoit/torbrowser,Shondoit/torbrowser,Shondoit/torbrowser