updated filename_invalid function

Author: jhpyle

Diff for: docassemble_base/docassemble/base/functions.py

@@ -121,7 +121,7 @@ def __str__(self):
 
 
 def filename_invalid(filename):
-    if '../' in filename:
+    if '../' in filename or filename.startswith('/'):
         return True
     if re.search(r'[^A-Za-z0-9\_\.\-\/ ]', filename):
         return True