detect all 0-alpha bmp and replace with all-255;

fix bug in reedbeta patch

stb_image.h

@@ -1,4 +1,4 @@
-/* stb_image - v2.06 - public domain image loader - http://nothings.org/stb_image.h
+/* stb_image - v2.08 - public domain image loader - http://nothings.org/stb_image.h
                                      no warranty implied; use at your own risk
 
    Do this:
@@ -205,6 +205,7 @@
                                                  Joseph Thomson
                                                  Phil Jordan
                                                  Nathan Reed
+                                                 urraka@github
 
 LICENSE
 
@@ -4112,20 +4113,21 @@ static int stbi__create_png_image_raw(stbi__png *a, stbi_uc *raw, stbi__uint32 r
             if (k > 6) *cur++ = scale * ((*in >> 1) & 0x01);
          }
          if (img_n != out_n) {
+            int q;
             // insert alpha = 255
             cur = a->out + stride*j;
             if (img_n == 1) {
-               for (i=x-1; i >= 0; --i) {
-                  cur[i*2+1] = 255;
-                  cur[i*2+0] = cur[i];
+               for (q=x-1; q >= 0; --q) {
+                  cur[q*2+1] = 255;
+                  cur[q*2+0] = cur[q];
                }
             } else {
                STBI_ASSERT(img_n == 3);
-               for (i=x-1; i >= 0; --i) {
-                  cur[i*4+3] = 255;
-                  cur[i*4+2] = cur[i*3+2];
-                  cur[i*4+1] = cur[i*3+1];
-                  cur[i*4+0] = cur[i*3+0];
+               for (q=x-1; q >= 0; --q) {
+                  cur[q*4+3] = 255;
+                  cur[q*4+2] = cur[q*3+2];
+                  cur[q*4+1] = cur[q*3+1];
+                  cur[q*4+0] = cur[q*3+0];
                }
             }
          }
@@ -4580,7 +4582,7 @@ static int stbi__shiftsigned(int v, int shift, int bits)
 static stbi_uc *stbi__bmp_load(stbi__context *s, int *x, int *y, int *comp, int req_comp)
 {
    stbi_uc *out;
-   unsigned int mr=0,mg=0,mb=0,ma=0, fake_a=0;
+   unsigned int mr=0,mg=0,mb=0,ma=0, all_a=255;
    stbi_uc pal[256][4];
    int psize=0,i,j,compress=0,width;
    int bpp, flip_vertically, pad, target, offset, hsz;
@@ -4629,8 +4631,7 @@ static stbi_uc *stbi__bmp_load(stbi__context *s, int *x, int *y, int *comp, int
                   mg = 0xffu <<  8;
                   mb = 0xffu <<  0;
                   ma = 0xffu << 24;
-                  fake_a = 1; // @TODO: check for cases like alpha value is all 0 and switch it to 255
-                  STBI_NOTUSED(fake_a);
+                  all_a = 0; // if all_a is 0 at end, then we loaded alpha channel but it was all 0
                } else {
                   mr = 31u << 10;
                   mg = 31u <<  5;
@@ -4741,6 +4742,7 @@ static stbi_uc *stbi__bmp_load(stbi__context *s, int *x, int *y, int *comp, int
                out[z+0] = stbi__get8(s);
                z += 3;
                a = (easy == 2 ? stbi__get8(s) : 255);
+               all_a |= a;
                if (target == 4) out[z++] = a;
             }
          } else {
@@ -4751,12 +4753,19 @@ static stbi_uc *stbi__bmp_load(stbi__context *s, int *x, int *y, int *comp, int
                out[z++] = STBI__BYTECAST(stbi__shiftsigned(v & mg, gshift, gcount));
                out[z++] = STBI__BYTECAST(stbi__shiftsigned(v & mb, bshift, bcount));
                a = (ma ? stbi__shiftsigned(v & ma, ashift, acount) : 255);
+               all_a |= a;
                if (target == 4) out[z++] = STBI__BYTECAST(a);
             }
          }
          stbi__skip(s, pad);
       }
    }
+   
+   // if alpha channel is all 0s, replace with all 255s
+   if (target == 4 && all_a == 0)
+      for (i=4*s->img_x*s->img_y-1; i >= 0; i -= 4)
+         out[i] = 255;
+
    if (flip_vertically) {
       stbi_uc t;
       for (j=0; j < (int) s->img_y>>1; ++j) {