Fix #13471. $().on(".xyz"...) should avoid later crash.

If the event type is an empty string we end up hanging in .off() which makes for
mighty hard debugging. Instead treat it as a no-op. Docs seem clear this is not
allowed.

src/event.js

@@ -66,6 +66,11 @@ jQuery.event = {
 			tmp = rtypenamespace.exec( types[t] ) || [];
 			type = origType = tmp[1];
 			namespaces = ( tmp[2] || "" ).split( "." ).sort();
+			
+			// There *must* be a type, no attaching namespace-only handlers
+			if ( !type ) {
+				continue;
+			}
 
 			// If event changes its type, use the special event handlers for the changed type
 			special = jQuery.event.special[ type ] || {};