Silence a compiler warning

Signed-off-by: falkTX <falktx@falktx.com>

dgl/src/nanovg/stb_image.h

@@ -4395,7 +4395,7 @@ static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
                if (!(s->img_n & 1)) return stbi__err("tRNS with alpha","Corrupt PNG");
                if (c.length != (stbi__uint32) s->img_n*2) return stbi__err("bad tRNS len","Corrupt PNG");
                has_trans = 1;
-               for (k=0; k < s->img_n; ++k)
+               for (k=0; k < s->img_n && k < 3; ++k)
                   tc[k] = (stbi_uc) (stbi__get16be(s) & 255) * stbi__depth_scale_table[depth]; // non 8-bit images will be larger
             }
             break;