Fix rpmfile fails to load localized RPM headers

#6
Return an array, and allow the user to deal with the issue.
There should not be any compatability options as we are the first to
use the library.

rpmfile/headers.py

@@ -312,6 +312,8 @@
 
 
 def extract_string(offset, count, store):
+    if count > 1:
+        return extract_array(offset, count, store)
     assert count == 1
     idx = store[offset:].index(b"\x00")
     return store[offset : offset + idx]