org-babel-ref-resolve: Search current buffer when FILE in FILE:REF does not exist

* lisp/ob-ref.el (org-babel-ref-resolve): Only search in other file
when FILE in FILE:REF exists.
* doc/org-manual.org (Passing arguments):
* etc/ORG-NEWS (Babel references =FILE:REFERENCE= now search current
buffer when =FILE= does not exist): Document the change.

Reported-by: Stefano Ghirlanda <dr.ghirlanda@gmail.com>
Link: https://orgmode.org/list/CAK_gY-Q4f82dbDQgyS+FfyeQaHAMXHqygq3e6ZsWnEj-+eoG9A@mail.gmail.com

doc/org-manual.org

@@ -17806,6 +17806,10 @@ from the reference.
 
 : :var NAME=FILE:REFERENCE
 
+When =FILE= does not exist, the reference is searched in the current
+file, using the verbatim reference.  This way,
+=:var table=tbl:example= will be searched inside the current buffer.
+
 Here are examples of passing values by reference:
 
 - table ::

etc/ORG-NEWS

@@ -13,6 +13,12 @@ Please send Org bug reports to mailto:emacs-orgmode@gnu.org.
 
 * Version 9.7 (not released yet)
 ** Important announcements and breaking changes
+*** Babel references =FILE:REFERENCE= now search current buffer when =FILE= does not exist
+
+When =FILE= does not exist, the reference is searched in the current
+file, using the verbatim reference.  This way,
+=:var table=tbl:example= will be searched inside the current buffer.
+
 *** New export option ~org-export-expand-links~
 
 The new option makes Org expand environment variables in link and INCLUDE paths.

lisp/ob-ref.el

@@ -156,8 +156,9 @@ Emacs Lisp representation of the value of the variable."
 	  (when (string-match "^\\(.+\\):\\(.+\\)$" ref)
 	    (setq split-file (match-string 1 ref))
 	    (setq split-ref (match-string 2 ref))
-	    (find-file split-file)
-	    (setq ref split-ref))
+            (when (file-exists-p split-file)
+	      (find-file split-file)
+	      (setq ref split-ref)))
 	  (org-with-wide-buffer
 	   (goto-char (point-min))
 	   (let* ((params (append args '((:results . "none"))))