Add exeption for when version metadata cannot be found for package (#3107)

Solves #3097

Already ran tests and lint.

langchain/__init__.py

@@ -55,7 +55,11 @@ from langchain.utilities.wikipedia import WikipediaAPIWrapper
 from langchain.utilities.wolfram_alpha import WolframAlphaAPIWrapper
 from langchain.vectorstores import FAISS, ElasticVectorSearch
 
-__version__ = metadata.version(__package__)
+try:
+    __version__ = metadata.version(__package__)
+except metadata.PackageNotFoundError:
+    # Case where package metadata is not available.
+    __version__ = ""
 del metadata  # optional, avoids polluting the results of dir(__package__)
 
 verbose: bool = False