Merge branch 'PHP-7.3'

* PHP-7.3:
  Fix #77479: imagewbmp() segfaults with very large images

ext/gd/libgd/gd_wbmp.c

@@ -100,6 +100,7 @@ void gdImageWBMPCtx (gdImagePtr image, int fg, gdIOCtx * out)
 	/* create the WBMP */
 	if ((wbmp = createwbmp (gdImageSX (image), gdImageSY (image), WBMP_WHITE)) == NULL) {
 		gd_error("Could not create WBMP");
+		return;
 	}
 
 	/* fill up the WBMP structure */

ext/gd/tests/bug77479.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Bug #77479 (imagewbmp() segfaults with very large image)
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
+?>
+--INI--
+memory_limit=-1
+--FILE--
+<?php
+$im = imagecreate(40000, 20000);
+imagecolorallocate($im, 0, 0, 0);
+imagewbmp($im, __DIR__ . '/77479.wbmp');
+?>
+===DONE===
+--EXPECTF--
+Warning: imagewbmp(): gd warning: product of memory allocation multiplication would exceed INT_MAX, failing operation gracefully
+ in %s on line %d
+
+Warning: imagewbmp(): Could not create WBMP in %s on line %d
+===DONE===
+--CLEAN--
+<?php
+@unlink(__DIR__ . '/77479.wbmp');
+?>