Description: fix invalid data read on bpl == -1
 Issue known as TALOS-2019-0821, or CVE-2019-5052.
Author: Sam Lantinga <slouken@libsdl.org>
Origin: upstream, https://hg.libsdl.org/SDL_image/rev/b920be2b3fc6
--- a/IMG_pcx.c	2019-07-27 13:21:35.678309318 -0300
+++ b/IMG_pcx.c	2019-07-27 13:21:35.678309318 -0300
@@ -148,7 +148,7 @@
         goto done;
 
     bpl = pcxh.NPlanes * pcxh.BytesPerLine;
-    if (bpl > surface->pitch) {
+    if (bpl < 0 || bpl > surface->pitch) {
         error = "bytes per line is too large (corrupt?)";
         goto done;
     }