store: raise ProgrammingError if unable to decode a storage path

Right now, the function magically return False which is dangerous, so let's
raise ProgrammingError.

Suggested by Augie in D5139.

Differential Revision: https://phab.mercurial-scm.org/D5264

mercurial/store.py

@@ -38,6 +38,8 b' def _matchtrackedpath(path, matcher):'
     elif path.startswith('meta/'):
         return matcher.visitdir(path[len('meta/'):-len('/00manifest.i')] or '.')
 
+    raise error.ProgrammingError("cannot decode path %s" % path)
+
 # This avoids a collision between a file named foo and a dir named
 # foo.i or foo.d
 def _encodedir(path):