Fix #167: uopz_set_return() overload confusion

If the first ZPP fails, clazz might be assigned, but is not nulled
afterwards.  To avoid potential BC breaks by swapping the ZPPs, we hack
in the nulling of the `clazz`, making use of the short-circuit behavior
of `&&`.

tests/bugs/gh167.phpt

@@ -0,0 +1,17 @@
+--TEST--
+uopz_set_return() overload confusion
+--EXTENSIONS--
+uopz
+--INI--
+uopz.disable=0
+--FILE--
+<?php
+class Foo {}
+function foo(): int {
+    return 42;
+}
+uopz_set_return("foo", function() {return 4711;}, true);
+var_dump(foo());
+?>
+--EXPECT--
+int(4711)

uopz.c

@@ -197,6 +197,7 @@ static PHP_FUNCTION(uopz_set_return)
 	uopz_disabled_guard();
 
 	if (uopz_parse_parameters("CSz|b", &clazz, &function, &variable, &execute) != SUCCESS &&
+		!((clazz = NULL)) &&
 		uopz_parse_parameters("Sz|b", &function, &variable, &execute) != SUCCESS) {
 		uopz_refuse_parameters(
 				"unexpected parameter combination, expected (class, function, variable [, execute]) or (function, variable [, execute])");