org.el (org-entry-get): Fix inheritance problem

* org.el (org-entry-get): Only try to combine file properties
with local properties when the property drawer contains such
local property, not when the property drawer exists.

Before the fix, `org-entry-get' behavior was inconsistent,
returning `nil' when looking for a property in a subtree with
no property drawer, and returning the global properties in a
subtree with a property drawer, independantly of whether this
property drawer contained a reference to the property we are checking
against or not.

As a side-effect, inheritance was broken for the case that
Ilya reported in commit 475f2f53, because `org-entry-get' returned
a value (with the global properties of the file) too early.

Thanks to Ilya for raising this bug and to Achim for pointing
out that the previous fix was wrong.

lisp/org.el

@@ -15324,7 +15324,13 @@ when a \"nil\" value can supersede a non-nil value higher up the hierarchy."
 	  (cdr (assoc property (org-entry-properties nil 'special property)))
 	(org-with-wide-buffer
 	 (let ((range (org-get-property-block)))
-	   (when (and range (not (eq (car range) (cdr range))))
+	   (when (and range (not (eq (car range) (cdr range)))
+		      (save-excursion
+		      	(goto-char (car range))
+		      	(re-search-forward
+		      	 (concat (org-re-property property) "\\|"
+				 (org-re-property (concat property "+")))
+			 (cdr range) t)))
 	     (let* ((props
 		     (list (or (assoc property org-file-properties)
 			       (assoc property org-global-properties)