Autocomplete (combobox demo): Blur the button on click to avoid a bug.

Thanks tyron.
(cherry picked from commit 401c91418c)

demos/autocomplete/combobox.html

@@ -101,6 +101,9 @@
 							return;
 						}
 
+						// work around a bug (likely same cause as #5265)
+						$( this ).blur();
+
 						// pass empty string as value to search for, displaying all results
 						input.autocomplete( "search", "" );
 						input.focus();