Allow for checking if the TimingData is empty.

AKA, no segments in use.

Again, this is mainly for the editor.

As for why a lowercase empty? Blame vectors.

src/TimingData.h

@@ -45,6 +45,8 @@ public:
 		return this->GetPreviousSegmentBeatAtRow(tst, BeatToNoteRow(beat), isDelay);
 	}
 	
+	bool empty() const;
+	
 	/**
 	 * @brief Sets up initial timing data with a defined offset.
 	 * @param fOffset the offset from the 0th beat. */