class Alpr: Set self.loaded to False before exception

There are currently [46 open issues related to `loaded`](https://github.com/openalpr/openalpr/search?p=2&q=loaded&type=issues).  Many of these [`AttributeError` issues](https://github.com/openalpr/openalpr/search?q=AttributeError&type=issues) are caused because `self.loaded` is only defined at the end of this method on (line 117).  If an exception is raised (like line 62, etc.) then `self.loaded` is _never_ defined so subsequent code fails when trying to determine if `Alpr` has successfully loaded.

Closes openalpr#311
Closes openalpr#414
Closes openalpr#426
Closes openalpr#461 
Closes openalpr#508
Closes openalpr#533
Closes openalpr#660
Closes openalpr#732
Closes openalpr#738
Closes openalpr#764
Closes openalpr#806
Closes openalpr#837 
Closes openalpr#913 
Closes openalpr#916 
Related to openalpr#555
Related to Homebrew/homebrew-core#89948

src/bindings/python/openalpr/openalpr.py

@@ -42,6 +42,7 @@ def __init__(self, country, config_file, runtime_dir):
         :param runtime_dir: The path to the OpenALPR runtime data directory
         :return: An OpenALPR instance
         """
+        self.loaded = False  # Will be set to True at the end of this method.
         country = _convert_to_charp(country)
         config_file = _convert_to_charp(config_file)
         runtime_dir = _convert_to_charp(runtime_dir)