fsck: fix error in reporting row number for timestamp errors

Since we process in chunks, we need to add "start" to the row number;
however, we don't need to use this when accessing data['timestamp']
(aka ts)

nilmdb/fsck/fsck.py

@@ -511,18 +511,20 @@ class Fsck(object):
                 # Verify that all timestamps are in range.
                 match = (ts < stime) | (ts >= etime)
                 if match.any():
-                    row = start + numpy.argmax(match)
+                    row = numpy.argmax(match)
                     raise FsckError("%s: data timestamp %d at row %d "
                                     "outside interval range [%d,%d)",
-                                    path, data['timestamp'][row], row,
+                                    path, ts[row], row + start,
                                     stime, etime)
 
                 # Verify that timestamps are monotonic
                 match = numpy.diff(ts) <= 0
                 if match.any():
-                    row = start + numpy.argmax(match)
-                    raise FsckError("%s: non-monotonic timestamp (%d -> %d) "
-                                    "at row %d", path, ts[row], ts[row+1], row)
+                    row = numpy.argmax(match)
+                    raise FsckError("%s: non-monotonic timestamp (%d -> %d)"
+                                    " at row %d", path, ts[row], ts[row+1],
+                                    row + start)
+
                 first_ts = ts[0]
                 if last_ts is not None and first_ts <= last_ts:
                     raise FsckError("%s: first interval timestamp %d is not "