TurboJPEG: Fix erroneous subsampling detection

... that caused some JPEG images with unusual sampling factors to be
misidentified as 4:4:4.  This led to a buffer overflow when attempting
to decompress some such images using tjDecompressToYUV*().

Regression introduced by 479501b07c

The correct behavior is for the TurboJPEG API to refuse to decompress
such images, which it did prior to the aforementioned commit.

Fixes #389

turbojpeg.c

@@ -368,9 +368,9 @@ static int getSubsamp(j_decompress_ptr dinfo)
           D_MAX_BLOCKS_IN_MCU / pixelsize[i] && i == TJSAMP_444) {
         int match = 0;
         for (k = 1; k < dinfo->num_components; k++) {
-          if (dinfo->comp_info[i].h_samp_factor ==
+          if (dinfo->comp_info[k].h_samp_factor ==
               dinfo->comp_info[0].h_samp_factor &&
-              dinfo->comp_info[i].v_samp_factor ==
+              dinfo->comp_info[k].v_samp_factor ==
               dinfo->comp_info[0].v_samp_factor)
             match++;
           if (match == dinfo->num_components - 1) {