[sfnt] allways copy file data to BytesIO, not just if deepcopy failed

on py27, calling deepcopy on a file object doesn't raise TypeError, but leaves
the duplicated file object in an inconsistent state:

https://travis-ci.org/fonttools/fonttools/jobs/474811063#L714

any operations on it will fail with 'ValueError: I/O operation on uninitialized object'.
Thus, for semplicity for now we always do a manual copy the file contents into an
in-memory BytesIO stream, rather than attempting to call deepcopy first.

Lib/fontTools/ttLib/sfnt.py

@@ -135,18 +135,14 @@ class SFNTReader(object):
 		obj = cls.__new__(cls)
 		for k, v in self.__dict__.items():
 			if k == "file":
-				try:
-					obj.file = deepcopy(v, memo)
-				except TypeError:
-					f = self.file
-					pos = f.tell()
-					f.seek(0)
-					buf = BytesIO(f.read())
-					f.seek(pos)
-					buf.seek(pos)
-					if hasattr(f, "name"):
-						buf.name = f.name
-					obj.file = buf
+				pos = v.tell()
+				v.seek(0)
+				buf = BytesIO(v.read())
+				v.seek(pos)
+				buf.seek(pos)
+				if hasattr(v, "name"):
+					buf.name = v.name
+				obj.file = buf
 			else:
 				obj.__dict__[k] = deepcopy(v, memo)
 		return obj