batch.py: better error when missing API key or empty lines in input

Author: mtmail

Changes.txt

@@ -1,3 +1,10 @@
+unreleased
+  Batch example: Raise exception when API key fails (quota, missing API key)
+  Batch example: Raise exception when input file contains an empty line. Better
+    early than risking errors later during the async geocoding
+  Batch example: The CSV '1, "street,city"' were parsed as 3 columns, not the
+    expected 2 columns
+
 v2.2.0 Fri 05 May 2023
   Using requests > 2.26 , pyopenssl no longer a dependency
   Allow setting the http protocol to make API requests (less secure)