[lldb-dap] Fix broken tests with commanEscapePrefix="" (#137384)

* Fix broken tests that use commanEscapePrefix="", in my case
`TestDAP_stackTraceMissingModule.test_missingModule`

Author: eronnen

lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py

@@ -860,7 +860,7 @@ def request_launch(
         args_dict["enableAutoVariableSummaries"] = enableAutoVariableSummaries
         args_dict["enableSyntheticChildDebugging"] = enableSyntheticChildDebugging
         args_dict["displayExtendedBacktrace"] = displayExtendedBacktrace
-        if commandEscapePrefix:
+        if commandEscapePrefix is not None:
             args_dict["commandEscapePrefix"] = commandEscapePrefix
         command_dict = {"command": "launch", "type": "request", "arguments": args_dict}
         response = self.send_recv(command_dict)