ext/odbc: fix cond for SQL_NO_TOTAL that led to single byte buffer

The ternary condition here was inverted, which could lead to a single
byte buffer being used, which is insufficient for anything. Fix it by
making the conditionals clearer.

Fixes GH-23443.

Author: NattyNarwhal

ext/pdo_odbc/odbc_stmt.c

@@ -763,10 +763,14 @@ static int odbc_stmt_get_col(pdo_stmt_t *stmt, int colno, zval *result, enum pdo
 			 * changed from 256 byte to LONG_COLUMN_BUFFER_SIZE.
 			 */
 			ssize_t to_fetch_len;
-			if (orig_fetched_len == SQL_NO_TOTAL) {
-				to_fetch_len = C->datalen > (LONG_COLUMN_BUFFER_SIZE - 1) ? (LONG_COLUMN_BUFFER_SIZE - 1) : C->datalen;
-			} else {
+			if (orig_fetched_len == SQL_NO_TOTAL && C->datalen > (LONG_COLUMN_BUFFER_SIZE - 1)) {
+				to_fetch_len = C->datalen;
+			} else if (orig_fetched_len > 0) {
+				/* implicitly not SQL_NO_TOTAL, should be OK */
 				to_fetch_len = orig_fetched_len;
+			} else {
+				/* size must be > 0 to actually get data */
+				to_fetch_len = (LONG_COLUMN_BUFFER_SIZE - 1);
 			}
 			ssize_t to_fetch_byte = to_fetch_len + 1;
 			char *buf2 = emalloc(to_fetch_byte);

ext/pdo_odbc/tests/gh23443.phpt

@@ -0,0 +1,24 @@
+--TEST--
+GH-23443 (infinite loop / 100% CPU when fetching a large nvarchar(max))
+--EXTENSIONS--
+pdo_odbc
+--SKIPIF--
+<?php
+require 'ext/pdo/tests/pdo_test.inc';
+PDOTest::skip();
+?>
+--FILE--
+<?php
+require 'ext/pdo/tests/pdo_test.inc';
+$db = PDOTest::test_factory('ext/pdo_odbc/tests/common.phpt');
+
+/*
+ * Likely depends on ZendMM page size + string overhead that affects long
+ * column buffer size 
+ */
+$n = 4499;
+$row = $db->query("SELECT REPLICATE(CAST(N'A' AS nvarchar(max)), $n) AS v")->fetch(PDO::FETCH_ASSOC);
+echo "ok\n";
+?>
+--EXPECT--
+ok