Clarify docstring: At EOF, GFile.readline() returns "".

Along the way, fix a comment about the same topic.

PiperOrigin-RevId: 311537677
Change-Id: I8dbd4fbf12f617efc5fdff0eb615337dc9c2fa8d

tensorflow/python/keras/layers/preprocessing/table_utils.py

@@ -144,7 +144,7 @@ def get_vocabulary_from_file(vocabulary_path, encoding="utf-8"):
   vocab = []
   with gfile.GFile(vocabulary_path, "r") as reader:
     while True:
-      # Get the next line, and break if it is None.
+      # Get the next line (incl. \n), and break if nothing is left to read.
       text = reader.readline()
       if not text:
         break

tensorflow/python/lib/io/file_io.py

@@ -165,7 +165,7 @@ class FileIO(object):
     self._read_buf.seek(offset)
 
   def readline(self):
-    r"""Reads the next line from the file. Leaves the '\n' at the end."""
+    r"""Reads the next line, keeping \n. At EOF, returns ''."""
     self._preread_check()
     return self._prepare_value(self._read_buf.readline())