Handle CLI arguments without a value in `OS.get_cmdline_args()` example

Command lines such as `--host --address 127.0.0.1` are now parsed as
`{"host": "", "address": "127.0.0.1"}`.

(cherry picked from commit 99d9228a2e)

doc/classes/OS.xml

@@ -152,6 +152,10 @@
 				    if argument.find("=") > -1:
 				        var key_value = argument.split("=")
 				        arguments[key_value[0].lstrip("--")] = key_value[1]
+				    else:
+				        # Options without an argument will be present in the dictionary,
+				        # with the value set to an empty string.
+				        arguments[argument.lstrip("--")] = ""
 				[/codeblock]
 			</description>
 		</method>