Add range checks to fix a few crash issues in stb_image issues 1289 and 1291

stb_image.h

@@ -1985,9 +1985,12 @@ static int stbi__build_huffman(stbi__huffman *h, int *count)
    int i,j,k=0;
    unsigned int code;
    // build size list for each symbol (from JPEG spec)
-   for (i=0; i < 16; ++i)
-      for (j=0; j < count[i]; ++j)
+   for (i=0; i < 16; ++i) {
+      for (j=0; j < count[i]; ++j) {
          h->size[k++] = (stbi_uc) (i+1);
+         if(k >= 257) return stbi__err("bad size list","Corrupt JPEG");
+      }
+   }
    h->size[k] = 0;
 
    // compute actual symbols (from jpeg spec)
@@ -2112,6 +2115,8 @@ stbi_inline static int stbi__jpeg_huff_decode(stbi__jpeg *j, stbi__huffman *h)
 
    // convert the huffman code to the symbol id
    c = ((j->code_buffer >> (32 - k)) & stbi__bmask[k]) + h->delta[k];
+   if(c < 0 || c >= 256) // symbol id out of bounds!
+       return -1;
    STBI_ASSERT((((j->code_buffer) >> (32 - h->size[c])) & stbi__bmask[h->size[c]]) == h->code[c]);
 
    // convert the id to a symbol
@@ -3103,6 +3108,7 @@ static int stbi__process_marker(stbi__jpeg *z, int m)
                sizes[i] = stbi__get8(z->s);
                n += sizes[i];
             }
+            if(n > 256) return stbi__err("bad DHT header","Corrupt JPEG"); // Loop over i < n would write past end of values!
             L -= 17;
             if (tc == 0) {
                if (!stbi__build_huffman(z->huff_dc+th, sizes)) return 0;