Add test for HEIC iloc extent_length underflow

Author: Oblivionsage

ext/exif/tests/heic_iloc_underflow.phpt

@@ -0,0 +1,19 @@
+--TEST--
+HEIC iloc extent_length underflow
+--EXTENSIONS--
+exif
+--FILE--
+<?php
+// Read valid HEIC file and patch iloc extent_length to 1
+$data = file_get_contents(__DIR__."/image029.heic");
+$data = substr_replace($data, "\x00\x00\x00\x01", 0x4f8, 4);
+file_put_contents(__DIR__."/heic_iloc_underflow.heic", $data);
+var_dump(exif_read_data(__DIR__."/heic_iloc_underflow.heic"));
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__."/heic_iloc_underflow.heic");
+?>
+--EXPECTF--
+Warning: exif_read_data(heic_iloc_underflow.heic): Invalid HEIF file in %s on line %d
+bool(false)