error in bibtex.el function bibtex-parse-buffers-stealthily

["numbchild@gmail.com" <numbchild@gmail.com>]

When I have a bibtex src block in Org-mode file.
Open the file will generate a buffer #<buffer
 *org-src-fontification:bibtex-mode*>.
This buffer caused function bibtex-parse-buffers-stealthily  timer error.
Here is the error:
```
Error running timer ‘bibtex-parse-buffers-stealthily’: (wrong-type-argument
number-or-marker-p nil)

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
  bibtex-parse-keys(t)
  bibtex-parse-buffers-stealthily()
  apply(bibtex-parse-buffers-stealthily nil)
  timer-event-handler([t 0 0 0 t bibtex-parse-buffers-stealthily nil idle
0])
```
I have a bibtex src block in Org-mode file like this:

```
#+BEGIN_SRC bibtex
@article{FernandezGabbay2007,
  number = {6},
  volume = {205},
  pages = {917--965},
  year = {2007},
  journaltitle = {Information \& Computation},
  title = {Nominal rewriting},
  author = {Fernández, Maribel and Gabbay, Murdoch J.},
}
#+END_SRC
```


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