org-table: Fix column formulas

* lisp/org-table.el (org-table-recalculate): Fix column formulas in
  tables consisting of a single row group.

Reported-by: Michael Welle <mwe012008@gmx.net>
<http://permalink.gmane.org/gmane.emacs.orgmode/108886>

lisp/org-table.el

@@ -3199,8 +3199,8 @@ existing formula for column %s"
 		      (re-search-forward org-table-hline-regexp end t)
 		      (re-search-forward org-table-dataline-regexp end t))
 		 (setq beg (match-beginning 0)))
-		;; Just leave BEG where it is.
-		(t (setq beg (line-beginning-position)))))
+		;; Just leave BEG at the start of the table.
+		(t nil)))
 	   (setq beg (line-beginning-position)
 		 end (copy-marker (line-beginning-position 2))))
 	 (goto-char beg)

testing/lisp/test-org-table.el

@@ -1909,6 +1909,33 @@ is t, then new columns should be added as needed"
       (org-table-calc-current-TBLFM)
       (buffer-string)))))
 
+(ert-deftest test-org-table/single-rowgroup ()
+  "Test column formula in a table with a single rowgroup."
+  (should
+   (equal
+    "
+|---+---|
+| 1 | 0 |
+|---+---|
+#+TBLFM: $2=$1-1"
+    (org-test-with-temp-text "
+|---+---|
+| 1 |   |
+|---+---|
+<point>#+TBLFM: $2=$1-1"
+      (org-table-calc-current-TBLFM)
+      (buffer-string))))
+  (should
+   (equal
+    "
+| 1 | 0 |
+#+TBLFM: $2=$1-1"
+    (org-test-with-temp-text "
+| 1 |   |
+<point>#+TBLFM: $2=$1-1"
+      (org-table-calc-current-TBLFM)
+      (buffer-string)))))
+
 
 (provide 'test-org-table)