Fix #79068: gdTransformAffineCopy() changes interpolation method

We port
<9088591eae>.

NEWS

@@ -25,6 +25,8 @@ PHP                                                                        NEWS
   . Fixed bug #78923 (Artifacts when convoluting image with transparency).
     (wilson chen)
   . Fixed bug #79067 (gdTransformAffineCopy() may use unitialized values). (cmb)
+  . Fixed bug #79068 (gdTransformAffineCopy() changes interpolation method).
+    (cmb)
 
 - Libxml:
   . Fixed bug #79029 (Use After Free's in XMLReader / XMLWriter). (Laruence)

ext/gd/libgd/gd_interpolation.c

@@ -2351,7 +2351,7 @@ int gdTransformAffineCopy(gdImagePtr dst,
 	gdPointF pt, src_pt;
 	gdRect bbox;
 	int end_x, end_y;
-	gdInterpolationMethod interpolation_id_bak = GD_DEFAULT;
+	gdInterpolationMethod interpolation_id_bak = src->interpolation_id;
 	interpolation_method interpolation_bak;
 
 	/* These methods use special implementations */

ext/gd/tests/bug79068.phpt

@@ -0,0 +1,21 @@
+--TEST--
+Bug #79068 (gdTransformAffineCopy() changes interpolation method)
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+?>
+--FILE--
+<?php
+require_once __DIR__ . '/func.inc';
+
+$src = imagecreatetruecolor(100, 100);
+imagefilledrectangle($src, 0, 0, 99, 99, 0xffffff);
+imageline($src, 10, 10, 90, 90, 0x000000);
+imagesetinterpolation($src, IMG_BSPLINE);
+imageaffine($src, [1, 1, 1, 1, 1, 1]);
+$dst = imagerotate($src, 80, 0xffffff);
+
+test_image_equals_file(__DIR__ . '/bug79068.png', $dst);
+?>
+--EXPECT--
+The images are equal.