org: Fix potential modified src match-data issue

* lisp/org.el (org-fontify-meta-lines-and-blocks-1): When this is run on
a src block, a "leaky" major mode called in
`org-src-font-lock-fontify-block' can modify the match data.
This is problematic, as the match data already set is important for
font-lock.  To protect ourselves from this behaviour, we can wrap
`org-src-font-lock-fontify-block' in `save-match-data' to ensure that
the match data for the src block is conserved.

lisp/org.el

@@ -5289,7 +5289,8 @@ by a #."
 	    (org-remove-flyspell-overlays-in nl-before-endline end-of-endline)
 	    (cond
 	     ((and lang (not (string= lang "")) org-src-fontify-natively)
-	      (org-src-font-lock-fontify-block lang block-start block-end)
+	      (save-match-data
+                (org-src-font-lock-fontify-block lang block-start block-end))
 	      (add-text-properties bol-after-beginline block-end '(src-block t)))
 	     (quoting
 	      (add-text-properties