Validation of added headers, should contain key/val (2 parts)

backend/__init__.py

@@ -162,12 +162,14 @@ def changedetection_app(config=None, datastore_o=None):
             url = request.form.get('url').strip()
             tag = request.form.get('tag').strip()
 
+            # Extra headers
             form_headers = request.form.get('headers').strip().split("\n")
             extra_headers = {}
             if form_headers:
                 for header in form_headers:
                     if len(header):
                         parts = header.split(':', 1)
+                        if len(parts) == 2:
                             extra_headers.update({parts[0].strip(): parts[1].strip()})
 
             validators.url(url)  # @todo switch to prop/attr/observer