fixed: 'index out of range' if lemma <staff> is empty

- extended whole-measure test case to test this behaviour.
- commented out the last measure of this test case, because it’s
currently makes the test fail due to
DuChemin#11

massage/test/dat/TC.Variants.02.WholeMeasure.mei

@@ -96,6 +96,19 @@
 							</staff>
 						</measure>
 						<measure n="4">
+							<staff n="1"/>
+							<staff n="2">
+								<layer n="1">
+									<note dur="2" oct="4" pname="f" color="rgba(255,0,0,1)"/>
+									<note dur="2" oct="4" pname="f" color="rgba(255,0,0,1)"/>
+									<note dur="1" oct="4" pname="f" color="rgba(255,0,0,1)"/>
+								</layer>
+							</staff>
+							<staff n="3">
+								<layer/>
+							</staff>
+						</measure>
+						<!-- <measure n="5">
 							<staff n="1">
 								<layer n="1">
 									<mRest/>
@@ -113,7 +126,7 @@
 									<mRest/>
 								</layer>
 							</staff>
-						</measure>
+						</measure> -->
 					</section>
 				</score>
 			</mdiv>

massage/transform/alt.py

@@ -291,16 +291,19 @@ def wrap_whole_measure(staff, ALT_TYPE):
 	if ALT_TYPE == EMENDATION:
 		rich_wrapper_name = 'choice'	
 		rich_default_name = 'sic'
-	old_layer = staff.getChildrenByName('layer')[0]
-	notelist = get_descendants(old_layer, 'note rest space')
+	old_layers = staff.getChildrenByName('layer')
+	notelist = []
+	if len(old_layers) > 0:
+		old_layer = staff.getChildrenByName('layer')[0]
+		notelist.extend(get_descendants(old_layer, 'note rest space'))
+		staff.removeChild(old_layer)
 	new_layer = MeiElement('layer')
 	rich_wrapper = MeiElement(rich_wrapper_name)
 	rich_default_elem = MeiElement(rich_default_name)
 	for note in notelist:
 		rich_default_elem.addChild(note)
 	rich_wrapper.addChild(rich_default_elem)
 	new_layer.addChild(rich_wrapper)
-	staff.removeChild(old_layer)
 	staff.addChild(new_layer)
 	return rich_wrapper
 
@@ -327,7 +330,10 @@ def legal_with_lemma(staff, skip, dur):
 		"""
 		print "legal_with_lemma(" + str(staff) + ", " + str(skip) + ", " + str(dur) +")"
 		# print('legal_with_lemma(): ' + staff.getAttribute('n').value + ', s' + str(skip) + 'd' + str(dur))
-		old_layer = staff.getChildrenByName('layer')[0]
+		old_layers = staff.getChildrenByName('layer')
+		if len(old_layers) == 0:
+			return False
+		old_layer = old_layers[0]
 		notelist = get_descendants(old_layer, 'note rest space')
 		for note in notelist:
 			dur_attr = note.getAttribute('dur').getValue()