Fixes piskvorky#1401 , IS_SINGLE Function updated

gensim/models/phrases.py

@@ -104,6 +104,7 @@ def _is_single(obj):
     is a corpus if it is an iterable of documents.
     """
     obj_iter = iter(obj)
+    temp_iter = obj_iter
     try:
         peek = next(obj_iter)
         obj_iter = it.chain([peek], obj_iter)
@@ -113,9 +114,12 @@ def _is_single(obj):
     if isinstance(peek, string_types):
         # It's a document, return the iterator
         return True, obj_iter
+    if temp_iter == obj :
+        #Checking for iterator to the object    
+    	return False , obj_iter
     else:
         # If the first item isn't a string, assume obj is a corpus
-        return False, list(obj_iter)
+        return False, obj
 
 
 class SentenceAnalyzer(object):