Guard against num_components being a ridiculous value due to a corrupt header

ChangeLog.txt

@@ -30,6 +30,10 @@ so this was an attempt to make them happy.
 upper 64 bits of xmm6 and xmm7 on Win64 platforms, which violated the Win64
 calling conventions.
 
+[7] Fixed a regression caused by 1.2.0[6] in which decompressing corrupt JPEG
+images (specifically, images in which the component count was erroneously set
+to a large value) would cause libjpeg-turbo to segfault.
+
 
 1.2.0
 =====

jdmarker.c

@@ -323,14 +323,15 @@ get_sos (j_decompress_ptr cinfo)
 
   /* Collect the component-spec parameters */
 
-  for (i = 0; i < cinfo->num_components; i++)
+  for (i = 0; i < MAX_COMPS_IN_SCAN; i++)
     cinfo->cur_comp_info[i] = NULL;
 
   for (i = 0; i < n; i++) {
     INPUT_BYTE(cinfo, cc, return FALSE);
     INPUT_BYTE(cinfo, c, return FALSE);
     
-    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
+    for (ci = 0, compptr = cinfo->comp_info;
+	 ci < cinfo->num_components && ci < MAX_COMPS_IN_SCAN;
 	 ci++, compptr++) {
       if (cc == compptr->component_id && !cinfo->cur_comp_info[ci])
 	goto id_found;