Fix #77200: imagecropauto(…, GD_CROP_SIDES) crops left but not right

We apply the upstream patch[1].

[1] <libgd/libgd@6613094>

NEWS

@@ -12,6 +12,8 @@ PHP                                                                        NEWS
 - GD:
   . Fixed bug #77195 (Incorrect error handling of imagecreatefromjpeg()). (cmb)
   . Fixed bug #77198 (auto cropping has insufficient precision). (cmb)
+  . Fixed bug #77200 (imagecropauto(…, GD_CROP_SIDES) crops left but not right).
+    (cmb)
 
 - Sockets:
   . Fixed bug #77136 (Unsupported IPV6_RECVPKTINFO constants on macOS).

ext/gd/libgd/gd_crop.c

@@ -315,7 +315,7 @@ static int gdGuessBackgroundColorFromCorners(gdImagePtr im, int *color)
 	} else if (tl == tr  || tl == bl || tl == br) {
 		*color = tl;
 		return 2;
-	} else if (tr == bl) {
+	} else if (tr == bl || tr == br) {
 		*color = tr;
 		return 2;
 	} else if (br == bl) {

ext/gd/tests/bug77200.phpt

@@ -0,0 +1,37 @@
+--TEST--
+Bug #77200 (imagecropauto(…, GD_CROP_SIDES) crops left but not right)
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+if (!GD_BUNDLED) die('upstream bugfix has not been released');
+?>
+--FILE--
+<?php
+
+$orig = imagecreatetruecolor(8, 8);
+$red = imagecolorallocate($orig, 255, 0, 0);
+$green = imagecolorallocate($orig, 0, 255, 0);
+$blue = imagecolorallocate($orig, 0, 0, 255);
+
+imagefilledrectangle($orig, 0, 0, 3, 3, $green); // tl
+imagefilledrectangle($orig, 4, 0, 7, 3, $red);   // tr
+imagefilledrectangle($orig, 0, 4, 3, 7, $green); // bl
+imagefilledrectangle($orig, 4, 4, 7, 7, $blue);  // br
+
+$cropped = imagecropauto($orig, IMG_CROP_SIDES);
+var_dump(imagesx($cropped));
+
+imagefilledrectangle($orig, 0, 0, 3, 3, $red);   // tl
+imagefilledrectangle($orig, 4, 0, 7, 3, $green); // tr
+imagefilledrectangle($orig, 0, 4, 3, 7, $blue);  // bl
+imagefilledrectangle($orig, 4, 4, 7, 7, $green); // br
+
+$cropped = imagecropauto($orig, IMG_CROP_SIDES);
+var_dump(imagesx($cropped));
+
+?>
+===DONE===
+--EXPECT--
+int(4)
+int(4)
+===DONE===