Fix #71316: libpng warning from imagecreatefromstring

ext/gd/libgd/gd_png.c

@@ -71,6 +71,11 @@ static void gdPngErrorHandler (png_structp png_ptr, png_const_charp msg)
 
 	longjmp (jmpbuf_ptr->jmpbuf, 1);
 }
+
+static void gdPngWarningHandler (png_structp png_ptr, png_const_charp msg)
+{
+	gd_error_ex(GD_WARNING, "gd-png: libpng warning: %s", msg);
+}
 #endif
 
 static void gdPngReadData (png_structp png_ptr, png_bytep data, png_size_t length)
@@ -152,7 +157,7 @@ gdImagePtr gdImageCreateFromPngCtx (gdIOCtx * infile)
 	}
 
 #ifdef PNG_SETJMP_SUPPORTED
-	png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, &jbw, gdPngErrorHandler, NULL);
+	png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, &jbw, gdPngErrorHandler, gdPngWarningHandler);
 #else
 	png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
 #endif
@@ -494,7 +499,7 @@ void gdImagePngCtxEx (gdImagePtr im, gdIOCtx * outfile, int level, int basefilte
 #ifdef PNG_SETJMP_SUPPORTED
 	jmpbuf_wrapper jbw;
 
-	png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, &jbw, gdPngErrorHandler, NULL);
+	png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, &jbw, gdPngErrorHandler, gdPngWarningHandler);
 #else
 	png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
 #endif

ext/gd/tests/bug71316.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Bug #71316 (libpng warning from imagecreatefromstring)
+--SKIPIF--
+<?php
+if (!extension_loaded("gd")) die("skip gd extension not available");
+if (!(imagetypes() & IMG_PNG)) die("skip PNG support not available");
+if (!GD_BUNDLED && version_compare(GD_VERSION, "2.3.3", '<=')) {
+    die("skip test requires GD > 2.3.3");
+}
+?>
+--FILE--
+<?php
+var_dump(
+    @imagecreatefrompng(__DIR__ . '/bug71316.png')
+);
+?>
+--EXPECTF--
+resource(%d) of type (gd)