community[patch]: avoid KeyError when language not in LANGUAGE_SEGMENTERS (#15212)

**Description:**

Handle unsupported languages in same way as when none is provided 
 
**Issue:**

The following line will throw a KeyError if the language is not
supported.
```python
self.Segmenter = LANGUAGE_SEGMENTERS[language]
```
E.g. when using `Language.CPP` we would get `KeyError: <Language.CPP:
'cpp'>`

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/community/langchain_community/document_loaders/parsers/language/language_parser.py

@@ -97,6 +97,8 @@ class LanguageParser(BaseBlobParser):
             language: If None (default), it will try to infer language from source.
             parser_threshold: Minimum lines needed to activate parsing (0 by default).
         """
+        if language and language not in LANGUAGE_SEGMENTERS:
+            raise Exception(f"No parser available for {language}")
         self.language = language
         self.parser_threshold = parser_threshold