importers: Catch and handle CSV parse errors in can_import.

import2ledger bailed on one of these exceptions when trying to import
a recent XLS file that had a null byte on a line.

import2ledger/importers/_csv.py

@@ -63,8 +63,12 @@ class CSVImporterBase:
 
     @classmethod
     def can_import(cls, input_file):
-        _, fields = cls._read_header(input_file)
-        return cls._NEEDED_KEYS.issubset(fields or ())
+        try:
+            _, fields = cls._read_header(input_file)
+        except csv.Error:
+            return False
+        else:
+            return cls._NEEDED_KEYS.issubset(fields or ())
 
     def __init__(self, input_file):
         self.entry_seed, fields = self._read_header(input_file)

setup.py

@@ -30,7 +30,7 @@ REQUIREMENTS['tests_require'] = [
 setup(
     name='import2ledger',
     description="Import different sources of financial data to Ledger",
-    version='0.3',
+    version='0.4',
     author='Brett Smith',
     author_email='brettcsmith@brettcsmith.org',
     license='GNU AGPLv3+',