Improve fix for bug #73807

At least on some architectures memmove() on FreeBSD does not
short-curcuit if src==dst. Check for it explicitly to avoid
quadratic copying.

Author: nikic

main/php_variables.c

@@ -311,7 +311,7 @@ static inline int add_post_vars(zval *arr, post_var_data_t *vars, zend_bool eof)
 		}
 	}
 
-	if (!eof) {
+	if (!eof && ZSTR_VAL(vars->str.s) != vars->ptr) {
 		memmove(ZSTR_VAL(vars->str.s), vars->ptr, ZSTR_LEN(vars->str.s) = vars->end - vars->ptr);
 	}
 	return SUCCESS;