fix mistral dashbaord workflow execution form bug

fix a bug that when a workflow has no input params, execution form
will has a requried field with empty label

Close-bug:#1786723
Change-Id: I49b2125ef649e94e210ff5df739684626c175172

mistraldashboard/workflows/forms.py

@@ -45,6 +45,7 @@ class ExecuteForm(forms.SelfHandlingForm):
         for entry in list.split(","):
             label, _, default = entry.partition("=")
             label = label.strip()
+            if label != '':
                 self.workflow_parameters.append(label)
                 if default == "None":
                     default = None