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

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

(cherry picked from commit 9c6c2387b920b3a0bc1d6b57f8ad6ca2a1b7ece4)
(cherry picked from commit c7133a67207b257abb54aa001fe8428b163a8ace)

src/video/stb_image.h

@@ -1123,7 +1123,7 @@ 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) &&
@@ -1146,7 +1146,7 @@ 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;
@@ -1304,7 +1304,7 @@ 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)
@@ -1975,7 +1975,7 @@ 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");
@@ -5297,10 +5297,10 @@ 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;
@@ -7217,7 +7217,10 @@ 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");
 }