Try to be more pythonic for size checks

Slight behoavior differences between all() and != (None,None):
- all() requires ALL terms to be not None (where (None, "cm") would pass
  != (None,None))
- all() checks for None or 0 or empty string
	No empty unit is supported (yet)
	A size of 0 does not really makes sense (and currently is passed
since it is the string "0")

patacrep/songs/chordpro/__init__.py

@@ -210,10 +210,11 @@ class Chordpro2LatexSong(ChordproSong):
             return ""
         if size[0] == "size":
             sizelist = []
-            if size[1] != (None, None):
-                sizelist.append("width=" + "".join(size[1]))
-            if size[2] != (None, None):
-                sizelist.append("height=" + "".join(size[2]))
+            width, height = size[1:3]
+            if all(width):
+                sizelist.append("width=" + "".join(width))
+            if all(height):
+                sizelist.append("height=" + "".join(height))
             return ", ".join(sizelist)
         if size[0] == "scale":
             return "scale=" + size[1]
@@ -251,11 +252,12 @@ class Chordpro2ChordproSong(ChordproSong):
             return ""
         if size[0] == "size":
             text = "size="
-            if size[1] != (None, None):
-                text += "".join(size[1])
+            width, height = size[1:3]
+            if all(width):
+                text += "".join(width)
             text += "x"
-            if size[2] != (None, None):
-                text += "".join(size[2])
+            if all(height):
+                text += "".join(height)
             return text
         if size[0] == "scale":
             return "scale=" + size[1]