Checksum mismatch when checksum is not properly base64 padded

[dsanghan]

In + (nullable NSData *)readArmored:(NSString *)string error:(NSError * __autoreleasing _Nullable *)error:

let readChecksumData = [[NSData alloc] initWithBase64EncodedString:checksumString options:0];

The checksumString will need to be properly padded to convert to data.
https://stackoverflow.com/questions/21406482/nsdata-wont-accept-valid-base64-encoded-string

After fixing that, sometimes it also has false mismatches when the underlying signature is actually correct.

Example with eml / signature / public key:
ChecksumMismatch.zip