[enh] stop searx when an engine raise an SyntaxError exception (#2177)
[enh] stop searx when an engine raise an SyntaxError exception (#2177)

and some other exceptions:
* KeyboardInterrupt
* SystemExit
* RuntimeError
* SystemError
* ImportError: an engine with an unmet dependency will stop everything.
dalf/searx,dalf/searx,dalf/searx,dalf/searx