micropolis: Improve decode a little more.

seekToPattern() can skip the index hole if it doesn't find the
SYNC pattern.  If this happens too close to the end of the flux
stream, it can result in a conflicted sector.  In this case,
discard the sector.

arch/micropolis/decoder.cc

@@ -103,6 +103,15 @@ public:
 			clock = seekToPattern(SECTOR_SYNC_PATTERN);
 		}
 
+		_sector->headerStartTime = tell().ns();
+
+		/* seekToPattern() can skip past the index hole, if this happens
+		 * too close to the end of the Fluxmap, discard the sector.
+		 */
+		if (_sector->headerStartTime > (getFluxmapDuration() - 12.5e6)) {
+			return 0;
+		}
+
 		return clock;
 	}