Catch errors when responding on proxy error

Signed-off-by: Lauri Nevala <lauri.nevala@gmail.com>

src/main/lens-proxy.ts

@@ -131,7 +131,11 @@ export class LensProxy {
           }
         }
       }
+      try {
         res.writeHead(500).end("Oops, something went wrong.")
+      } catch (e) {
+        // Can't send headers. Probably app is closing.
+      }
     })
 
     return proxy;