Lossless: Fix innocuous UBSan warnings

Author: dcommander

jclossls.c

@@ -256,8 +256,9 @@ METHODDEF(void)
 simple_downscale(j_compress_ptr cinfo,
                  _JSAMPROW input_buf, _JSAMPROW output_buf, JDIMENSION width)
 {
-  while (width--)
+  do {
     *output_buf++ = (_JSAMPLE)RIGHT_SHIFT(*input_buf++, cinfo->Al);
+  } while (--width);
 }
 
 

jddiffct.c

@@ -196,7 +196,8 @@ decompress_data(j_decompress_ptr cinfo, _JSAMPIMAGE output_buf)
     }
 
     /* Account for restart interval (no-op if not using restarts) */
-    diff->restart_rows_to_go--;
+    if (cinfo->restart_interval)
+      diff->restart_rows_to_go--;
 
     /* Completed an MCU row, but perhaps not an iMCU row */
     diff->MCU_ctr = 0;

jdlossls.c

@@ -216,16 +216,18 @@ METHODDEF(void)
 simple_upscale(j_decompress_ptr cinfo,
                JDIFFROW diff_buf, _JSAMPROW output_buf, JDIMENSION width)
 {
-  while (width--)
+  do {
     *output_buf++ = (_JSAMPLE)(*diff_buf++ << cinfo->Al);
+  } while (--width);
 }
 
 METHODDEF(void)
 noscale(j_decompress_ptr cinfo,
         JDIFFROW diff_buf, _JSAMPROW output_buf, JDIMENSION width)
 {
-  while (width--)
+  do {
     *output_buf++ = (_JSAMPLE)(*diff_buf++);
+  } while (--width);
 }