Use a warnings instead of raising exception

where zlib error is detected before the CRC checksum.

pdfminer/pdftypes.py

@@ -1,11 +1,13 @@
 import zlib
+import warnings
 import logging
 import io
 from .lzw import lzwdecode
 from .ascii85 import ascii85decode
 from .ascii85 import asciihexdecode
 from .runlength import rldecode
 from .ccitt import ccittfaxdecode
+from .pdfdocument import PDFEncryptionError
 from .psparser import PSException
 from .psparser import PSObject
 from .psparser import LIT
@@ -203,7 +205,7 @@ def decompress_corrupted(data):
     except zlib.error:
         # Let the error propagates if we're not yet in the CRC checksum
         if i < len(data) - 3:
-            raise
+            warnings.warn("Data-loss while decompressing corrupted data", PDFEncryptionError)
     return result_str