Print objects with null hash table like others in print_r

Noticed when working on subsequent commits for SplFixedArray.
Make whether zend_get_properties_for returns null or an empty array
invisible to the end user - it would be always be a non-null array for
user-defined classes.

Noticed when working on SplFixedArray changes, e.g. in
ext/spl/tests/SplFixedArray__construct_param_null.phpt

Author: TysonAndre

Zend/tests/function_arguments/sensitive_parameter_value.phpt

@@ -31,6 +31,8 @@ object(SensitiveParameterValue)#%d (0) {
 object(SensitiveParameterValue)#%d (%d) refcount(%d){
 }
 SensitiveParameterValue Object
+(
+)
 
 # var_export()
 \SensitiveParameterValue::__set_state(array(

Zend/zend.c

@@ -507,6 +507,7 @@ static void zend_print_zval_r_to_buf(smart_str *buf, zval *expr, int indent) /*
 				}
 
 				if ((properties = zend_get_properties_for(expr, ZEND_PROP_PURPOSE_DEBUG)) == NULL) {
+					print_hash(buf, (HashTable*) &zend_empty_array, indent, 1);
 					break;
 				}