Minor improvement of the randomcase tamper script

tamper/randomcase.py

@@ -44,11 +44,15 @@ def tamper(payload, **kwargs):
             word = match.group()
 
             if word.upper() in kb.keywords:
-                _ = str()
+                while True:
+                    _ = ""
 
                     for i in xrange(len(word)):
                         _ += word[i].upper() if randomRange(0, 1) else word[i].lower()
 
+                    if len(_) > 1 and _ not in (_.lower(), _.upper()):
+                        break
+
                 retVal = retVal.replace(word, _)
 
     return retVal