Fix ATTR_ORACLE_NULLS with PARAM_ZVAL

PARAM_ZVAL with a STR result should be treated the same way as
PARAM_STR in this regard.

Author: nikic

ext/pdo/pdo_stmt.c

@@ -520,6 +520,12 @@ static inline void fetch_value(pdo_stmt_t *stmt, zval *dest, int colno, int *typ
 		case PDO_PARAM_ZVAL:
 			if (value && value_len == sizeof(zval)) {
 				ZVAL_COPY_VALUE(dest, (zval *)value);
+
+				if (Z_TYPE_P(dest) == IS_STRING && Z_STRLEN_P(dest) == 0
+						&& stmt->dbh->oracle_nulls == PDO_NULL_EMPTY_STRING) {
+					zval_ptr_dtor_str(dest);
+					ZVAL_NULL(dest);
+				}
 			} else {
 				ZVAL_NULL(dest);
 			}

ext/pdo_mysql/tests/pdo_mysql_attr_oracle_nulls.phpt

@@ -112,11 +112,11 @@ array(1) {
     ["z"]=>
     NULL
     ["a"]=>
-    string(0) ""
+    NULL
     ["b"]=>
     string(1) " "
     ["c"]=>
-    string(0) ""
+    NULL
     ["d"]=>
     string(2) " d"
     ["e"]=>
@@ -131,11 +131,11 @@ array(1) {
     ["z"]=>
     NULL
     ["a"]=>
-    string(0) ""
+    NULL
     ["b"]=>
     string(1) " "
     ["c"]=>
-    string(0) ""
+    NULL
     ["d"]=>
     string(2) " d"
     ["e"]=>