webrepl_cli.py: Allow empty target name to mean default (root) dir.

E.g.

webrepl_cli.py foo.txt 192.168.4.1:

Author: Paul Sokolovsky

webrepl_cli.py

@@ -142,6 +142,8 @@ def error(msg):
 
 def parse_remote(remote):
     host, fname = remote.rsplit(":", 1)
+    if fname = "":
+        fname = "/"
     port = 8266
     if ":" in host:
         host, port = remote.split(":")