fix backtracking hang in hstore literal parser

fix backtracking hang in hstore literal parser

Fixed regular expression in the pure Python hstore result processor,
used when ``use_native_hstore=False`` is set, which could hang on
malformed hstore text containing unterminated quoted segments with
backslashes.  Pull request courtesy dxbjavid.

Fixes: #13370
Closes: #13371
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/13371
Pull-request-sha: f5eddae11c435c78f326b70a15357cbaf6d09337

Change-Id: I0d2d7565dc88f56a73b41e2ad20ca1c5a6f738bb
(cherry picked from commit 0c38dfff3025176324996970dfb0c0f3e05ff28d)