webpack: Close potential race condition leaking webpack-dev-server process.
webpack: Close potential race condition leaking webpack-dev-server process.

This exchanges a race condition where webpack-dev-server might not be
stopped on a poorly timed KeyboardInterrupt for a less bad race
condition where we might get an UnboundLocalError.

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulipchat.com>

synicalsyntax/zulip,andersk/zulip,rht/zulip,hackerkid/zulip,rht/zulip,shubhamdhama/zulip,rishig/zulip,synicalsyntax/zulip,tommyip/zulip,brainwane/zulip,kou/zulip,eeshangarg/zulip,showell/zulip,hackerkid/zulip,tommyip/zulip,brainwane/zulip,kou/zulip,rishig/zulip,tommyip/zulip,andersk/zulip,rht/zulip,rishig/zulip,rishig/zulip,synicalsyntax/zulip,punchagan/zulip,showell/zulip,zulip/zulip,kou/zulip,brainwane/zulip,timabbott/zulip,tommyip/zulip,kou/zulip,shubhamdhama/zulip,shubhamdhama/zulip,timabbott/zulip,kou/zulip,punchagan/zulip,zulip/zulip,brainwane/zulip,eeshangarg/zulip,rishig/zulip,punchagan/zulip,rishig/zulip,rht/zulip,punchagan/zulip,rishig/zulip,tommyip/zulip,andersk/zulip,punchagan/zulip,zulip/zulip,andersk/zulip,timabbott/zulip,showell/zulip,synicalsyntax/zulip,hackerkid/zulip,eeshangarg/zulip,zulip/zulip,timabbott/zulip,showell/zulip,andersk/zulip,andersk/zulip,brainwane/zulip,synicalsyntax/zulip,eeshangarg/zulip,timabbott/zulip,tommyip/zulip,showell/zulip,eeshangarg/zulip,timabbott/zulip,shubhamdhama/zulip,synicalsyntax/zulip,rht/zulip,showell/zulip,hackerkid/zulip,shubhamdhama/zulip,timabbott/zulip,shubhamdhama/zulip,brainwane/zulip,tommyip/zulip,rht/zulip,zulip/zulip,rht/zulip,hackerkid/zulip,showell/zulip,brainwane/zulip,hackerkid/zulip,punchagan/zulip,andersk/zulip,synicalsyntax/zulip,shubhamdhama/zulip,zulip/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,kou/zulip,eeshangarg/zulip