Document the use of next to throw an exception when hitting EOF

Author: ghickman

git/repo/base.py

@@ -716,7 +716,7 @@ def blame_incremental(self, rev, file, **kwargs):
                 # Discard all lines until we find "filename" which is
                 # guaranteed to be the last line
                 while True:
-                    line = next(stream)
+                    line = next(stream)  # will fail if we reach the EOF unexpectedly
                     tag, value = line.split(b' ', 1)
                     if tag == b'filename':
                         orig_filename = value