picoev, x.vweb: small fixes and backport changes from vweb (#20584)

examples/pico/pico.v

@@ -50,6 +50,6 @@ fn callback(data voidptr, req picohttpparser.Request, mut res picohttpparser.Res
 
 fn main() {
 	println('Starting webserver on http://localhost:${port}/ ...')
-	mut server := picoev.new(port: port, cb: callback)
+	mut server := picoev.new(port: port, cb: callback)!
 	server.serve()
 }

examples/pico/raw_callback.v

@@ -12,7 +12,7 @@ fn main() {
 	mut pico := picoev.new(
 		port: port
 		raw_cb: handle_conn
-	)
+	)!
 	pico.serve()
 }