oc: Fix asCSSIdentifier in openchange_user_cleanup

The method lacked the check for the initial character, which adds an
underscore at the beginning of the strings that start with a digit.

Scripts/openchange_user_cleanup

@@ -268,6 +268,9 @@ def asCSSIdentifier(inputString):
 
     newChars = []
 
+    if str.isdigit(inputString[0]):
+        newChars.append("_")
+
     for c in inputString:
         if c in cssEscapingCharMap:
             newChars.append(cssEscapingCharMap[c])