Base64InputStream causes NullPointerException on some input

Certain (malformed?) input to Base64InputStream causes a NullPointerException in Base64.decode.

The exception occurs when Base64.decode is entered with the following conditions:

• buffer is null
• modulus is 3 from a previous entry.
• inAvail is -1 because Base64InputStream.read reached EOF on line 150.

Under these conditions, Base64.decode reaches line 581 with buffer still null and throws a NullPointerException.

Here is some input data that will trigger it:
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Say this is read from file with a byte[] of size 1024 using Base64InputStream.read(byte[]). In the first iteration, all 1190 bytes get read into buf, then it enters Base64.setInitialBuffer and assigns the byte[1024] to buffer and does a round of decoding. When it then enters Base64.readResults on line 162 in Base64InputStream, it sets buffer to null, modulus has the left-over value 3, and the NPE occurs the next iteration.

Base64InputStream could avoid this by returning right away on EOF (-1), but I think the real fix needs to happen in Base64 since it this same situation could be created by direct use. My guess is either more needs to happen in the body of the if on line 542 (set modulus to 0?) or the condition on line 573 is flawed and needs adjusting.