suricatasc: Don't process empty cmds

(cherry picked from commit 6b3dbaa2f2)

python/suricata/sc/suricatasc.py

@@ -256,6 +256,8 @@ class SuricataSC:
                     command = input(">>> ").strip()
                 if command == "quit":
                     break
+                if len(command.strip()) == 0:
+                    continue
                 try:
                     cmd, arguments = self.parse_command(command)
                 except SuricataCommandException as err: