Spreadsheet: Don't assume every last row filed has a formula

In a recent patch we have introduced names for all fields in the last
row.  This has lead to a bug, that Org thinks there might be a field
formula associated with those fields.  Now we check if there really is
one, and only in this case ask to overwrite it with a column formula.

Report by Henry Atting.

lisp/ChangeLog

@@ -1,5 +1,8 @@
 2008-12-22  Carsten Dominik  <carsten.dominik@gmail.com>
 
+	* org-table.el (org-table-get-formula): Only ask to overwrite
+	field formula if there really is one.
+
 	* org-id.el (org-id-find): Allow the ID to be a symbol or a
 	number, by converting these to a string.
 

lisp/org-table.el

@@ -1722,13 +1722,14 @@ When NAMED is non-nil, look for a named equation."
 	 (ref (format "@%d$%d" (org-table-current-dline)
 		      (org-table-current-column)))
 	 (refass (assoc ref stored-list))
+	 (nameass (assoc name stored-list))
 	 (scol (if named
 		   (if (and name (not (string-match "^LR[0-9]+$" name)))
 		       name
 		     ref)
 		 (int-to-string (org-table-current-column))))
-	 (dummy (and (or name refass) (not named)
-		     (not (y-or-n-p "Replace field formula with column formula? " ))
+	 (dummy (and (or nameass refass) (not named)
+		     (not (y-or-n-p "Replace existing field formula with column formula? " ))
 		     (error "Abort")))
 	 (name (or name ref))
 	 (org-table-may-need-update nil)