Add missing parseAndCombineSignatures call

For some reason this was missing from the single-byte read() method
of the SignatureInputStream, causing issues if draining the stream
byte by byte

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/SignatureInputStream.java

@@ -67,6 +67,7 @@ public abstract class SignatureInputStream extends FilterInputStream {
             final int data = super.read();
             final boolean endOfStream = data == -1;
             if (endOfStream) {
+                parseAndCombineSignatures();
                 verifyOnePassSignatures();
                 verifyDetachedSignatures();
             } else {