Change if (stack) check to an assertion (#10090)

The code checks if stack is a NULL pointer. Below that if the
stack->next pointer is updated unconditionally. Therefore a call with a
NULL pointer will crash, even though the if (stack) check seems to show
the intent that it is valid to call the function with NULL.
The function is not meant to be called with NULL, so just ZEND_ASSERT
instead.

Author: ndossche

sapi/phpdbg/phpdbg_cmd.c

@@ -371,7 +371,9 @@ PHPDBG_API void phpdbg_param_debug(const phpdbg_param_t *param, const char *msg)
 
 /* {{{ */
 PHPDBG_API void phpdbg_stack_free(phpdbg_param_t *stack) {
-	if (stack && stack->next) {
+	ZEND_ASSERT(stack != NULL);
+
+	if (stack->next) {
 		phpdbg_param_t *remove = stack->next;
 
 		while (remove) {
@@ -422,10 +424,9 @@ PHPDBG_API void phpdbg_stack_free(phpdbg_param_t *stack) {
 				remove = next;
 			else break;
 		}
-	}
 
-
-	stack->next = NULL;
+		stack->next = NULL;
+	}
 } /* }}} */
 
 /* {{{ */