stb_image.h: apply patches from mainstream PRs 1839, 1862 and 1863.

Patches authored by @NBickford-NV to fix mainstream issues 1838, 1860,
1861.

Author: sezero

src/stb_image.h

@@ -1110,7 +1110,7 @@ static int stbi__mad3sizes_valid(int a, int b, int c, int add)
 }
 
 // returns 1 if "a*b*c*d + add" has no negative terms/factors and doesn't overflow
-#if !defined(STBI_NO_LINEAR) || !defined(STBI_NO_HDR) || !defined(STBI_NO_PNM)
+#if !defined(STBI_NO_LINEAR) || !defined(STBI_NO_HDR) || !defined(STBI_NO_PNM) || !defined(STBI_NO_PNG) || !defined(STBI_NO_PSD)
 static int stbi__mad4sizes_valid(int a, int b, int c, int d, int add)
 {
    return stbi__mul2sizes_valid(a, b) && stbi__mul2sizes_valid(a*b, c) &&
@@ -1133,7 +1133,7 @@ static void *stbi__malloc_mad3(int a, int b, int c, int add)
    return stbi__malloc(a*b*c + add);
 }
 
-#if !defined(STBI_NO_LINEAR) || !defined(STBI_NO_HDR) || !defined(STBI_NO_PNM)
+#if !defined(STBI_NO_LINEAR) || !defined(STBI_NO_HDR) || !defined(STBI_NO_PNM) || !defined(STBI_NO_PNG) || !defined(STBI_NO_PSD)
 static void *stbi__malloc_mad4(int a, int b, int c, int d, int add)
 {
    if (!stbi__mad4sizes_valid(a, b, c, d, add)) return NULL;
@@ -1287,7 +1287,7 @@ static stbi__uint16 *stbi__convert_8_to_16(stbi_uc *orig, int w, int h, int chan
    int img_len = w * h * channels;
    stbi__uint16 *enlarged;
 
-   enlarged = (stbi__uint16 *) stbi__malloc(img_len*2);
+   enlarged = (stbi__uint16 *) stbi__malloc_mad2(img_len, 2, 0);
    if (enlarged == NULL) return (stbi__uint16 *) stbi__errpuc("outofmem", "Out of memory");
 
    for (i = 0; i < img_len; ++i)
@@ -1956,7 +1956,7 @@ static stbi__uint16 *stbi__convert_format16(stbi__uint16 *data, int img_n, int r
    if (req_comp == img_n) return data;
    STBI_ASSERT(req_comp >= 1 && req_comp <= 4);
 
-   good = (stbi__uint16 *) stbi__malloc(req_comp * x * y * 2);
+   good = (stbi__uint16 *) stbi__malloc_mad4(req_comp, x, y, 2, 0);
    if (good == NULL) {
       STBI_FREE(data);
       return (stbi__uint16 *) stbi__errpuc("outofmem", "Out of memory");
@@ -5227,10 +5227,10 @@ static void stbi__de_iphone(stbi__png *z)
 
 static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp, unsigned int *palette_buffer, int palette_buffer_len)
 {
-   stbi_uc _palette[1024], pal_img_n=0;
+   stbi_uc _palette[1024]={0}, pal_img_n=0;
    stbi_uc *palette = _palette;
    stbi_uc has_trans=0, tc[3]={0};
-   stbi__uint16 tc16[3];
+   stbi__uint16 tc16[3]={0};
    stbi__uint32 ioff=0, idata_limit=0, i, pal_len=0;
    int first=1,k,interlace=0, color=0, is_iphone=0;
    stbi__context *s = z->s;
@@ -7147,7 +7147,10 @@ static void *stbi__load_gif_main_outofmem(stbi__gif *g, stbi_uc *out, int **dela
    STBI_FREE(g->background);
 
    if (out) STBI_FREE(out);
-   if (delays && *delays) STBI_FREE(*delays);
+   if (delays && *delays) {
+      STBI_FREE(*delays);
+      *delays = NULL;
+   }
    return stbi__errpuc("outofmem", "Out of memory");
 }
 
@@ -7182,19 +7185,15 @@ static void *stbi__load_gif_main(stbi__context *s, int **delays, int *x, int *y,
             stride = g.w * g.h * 4;
 
             if (out) {
-               void *tmp = (stbi_uc*) STBI_REALLOC_SIZED( out, out_size, layers * stride );
-               if (!tmp)
+               out = (stbi_uc*) STBI_REALLOC_SIZED( out, out_size, layers * stride );
+               if (!out)
                   return stbi__load_gif_main_outofmem(&g, out, delays);
-               else {
-                   out = (stbi_uc*) tmp;
-                   out_size = layers * stride;
-               }
+               out_size = layers * stride;
 
                if (delays) {
-                  int *new_delays = (int*) STBI_REALLOC_SIZED( *delays, delays_size, sizeof(int) * layers );
-                  if (!new_delays)
+                  *delays = (int*) STBI_REALLOC_SIZED( *delays, delays_size, sizeof(int) * layers );
+                  if (!*delays)
                      return stbi__load_gif_main_outofmem(&g, out, delays);
-                  *delays = new_delays;
                   delays_size = layers * sizeof(int);
                }
             } else {