Improve readability and flexibility of compatibility macros


git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@241 632fc199-4ca6-4c93-a231-07263d6284db
diff --git a/jdapistd.c b/jdapistd.c
index d8ea7ad..2343da5 100644
--- a/jdapistd.c
+++ b/jdapistd.c
@@ -204,7 +204,7 @@
   }
 
   /* Verify that at least one iMCU row can be returned. */
-  lines_per_iMCU_row = cinfo->max_v_samp_factor * _min_DCT_scaled_size;
+  lines_per_iMCU_row = cinfo->max_v_samp_factor * cinfo->_min_DCT_scaled_size;
   if (max_lines < lines_per_iMCU_row)
     ERREXIT(cinfo, JERR_BUFFER_SIZE);