[Qt] make PaymentServer::ipcParseCommandLine void

- the function only returned true, so make it void
- add a comment about payment request network detection

src/qt/paymentserver.h

@@ -59,7 +59,7 @@ class PaymentServer : public QObject
 public:
     // Parse URIs on command line
     // Returns false on error
-    static bool ipcParseCommandLine(int argc, char *argv[]);
+    static void ipcParseCommandLine(int argc, char *argv[]);
 
     // Returns true if there were URIs on the command line
     // which were successfully sent to an already-running