SDL_image: revert 'volatile' keyword removal commit a61c2fc38f for IMG_png.c:

From a4ae71897bcf1d8320a9bad9d39362d3977322e1 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Fri, 26 Jan 2024 11:11:02 +0300
Subject: [PATCH] revert 'volatile' keyword removal commit a61c2fc38f for
 IMG_png.c:

Silences gcc4.9 -Wclobbered warnings:

/tmp/SDL_image/src/IMG_png.c: In function 'IMG_LoadPNG_RW':
/tmp/SDL_image/src/IMG_png.c:240:18: warning: variable 'surface' might be clobbered by 'longjmp' or 'vfork' [-Wclobbered]
     SDL_Surface *surface;
                  ^
/tmp/SDL_image/src/IMG_png.c:247:16: warning: variable 'row_pointers' might be clobbered by 'longjmp' or 'vfork' [-Wclobbered]
     png_bytep *row_pointers;
                ^

Reference issue: https://github.com/libsdl-org/SDL_image/issues/416
---
 src/IMG_png.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/IMG_png.c b/src/IMG_png.c
index d09e312e..95b51462 100644
--- a/src/IMG_png.c
+++ b/src/IMG_png.c
@@ -237,14 +237,14 @@ SDL_Surface *IMG_LoadPNG_RW(SDL_RWops *src)
 {
     Sint64 start;
     const char *error;
-    SDL_Surface *surface;
+    SDL_Surface *volatile surface;
     png_structp png_ptr;
     png_infop info_ptr;
     png_uint_32 width, height;
     int bit_depth, color_type, interlace_type, num_channels;
     Uint32 format;
     SDL_Palette *palette;
-    png_bytep *row_pointers;
+    png_bytep *volatile row_pointers;
     int row, i;
     int ckey;
     png_color_16 *transv;