Fix unhandled exceptions in port-scanner. (eclipse#281)

In case IPv6 was disabled, `/proc/net/tcp6` will not exist.
(Probably IPv4 will be similar.)

Signed-off-by: Masaki Muranaka <monaka@monami-ya.com>

plugins/ports-plugin/src/port-scanner.ts

@@ -29,8 +29,12 @@ export class PortScanner {
         const ipConverter = new IpConverter();
         // connect to /proc/net/tcp and /proc/net/tcp6
         const command = new Command(__dirname);
-        const outputv4 = await command.exec(PortScanner.GRAB_PORTS_IPV4);
-        const outputv6 = await command.exec(PortScanner.GRAB_PORTS_IPV6);
+        const outputv4 = await command
+            .exec(PortScanner.GRAB_PORTS_IPV4)
+            .catch(e => { console.error(e); return ''; });
+        const outputv6 = await command
+            .exec(PortScanner.GRAB_PORTS_IPV6);
+            .catch(e => { console.error(e); return ''; });
 
         // assembe ipv4 and ipv6 output
         const output = `