Issue #17710: Fix pickle raising a SystemError on bogus input.

diff --cc Lib/pickle.py
index 998fce0a6bbf61915c2ee0f55c1e77e9b689b8f8,161c2e9e74b9b445f9471eee6e2b5a2ad68856d4..a4acbe941e0309b512f80563b9f50114c66f041a
--- 1/Lib/pickle.py
--- 2/Lib/pickle.py
+++ b/Lib/pickle.py
@@@ -902,11 -949,14 +902,11 @@@ class _Unpickler
      def load_string(self):
          orig = self.readline()
          rep = orig[:-1]
 -        for q in (b'"', b"'"): # double or single quote
 -            if rep.startswith(q):
 -                if len(rep) < 2 or not rep.endswith(q):
 -                    raise ValueError("insecure string pickle")
 -                rep = rep[len(q):-len(q)]
 -                break
 +        # Strip outermost quotes
-         if rep[0] == rep[-1] and rep[0] in b'"\'':
++        if len(rep) >= 2 and rep[0] == rep[-1] and rep[0] in b'"\'':
 +            rep = rep[1:-1]
          else:
 -            raise ValueError("insecure string pickle: %r" % orig)
 +            raise ValueError("insecure string pickle")
          self.append(codecs.escape_decode(rep)[0]
                      .decode(self.encoding, self.errors))
      dispatch[STRING[0]] = load_string

diff --cc Misc/NEWS
Simple merge

diff --cc Modules/_pickle.c
Simple merge