Make eof() consider padding when reading less than block size

[valga]

When reading from AES encrypting stream with chunk length < block size eof() returns true too early leaving a part of padding in the buffer.

[codecov[bot]]

Codecov Report

Merging #17 into master will not change coverage by %. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##              master       #17   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       113       116    +3     
===========================================
  Files             12        12           
  Lines            300       304    +4     
===========================================
+ Hits             300       304    +4     

Impacted Files	Coverage Δ	Complexity Δ
src/AesDecryptingStream.php	100.00% <100.00%> (ø)	21.00 <0.00> (ø)
src/AesEncryptingStream.php	100.00% <100.00%> (ø)	21.00 <2.00> (+3.00)
src/AesGcmDecryptingStream.php	100.00% <100.00%> (ø)	4.00 <0.00> (ø)
src/AesGcmEncryptingStream.php	100.00% <100.00%> (ø)	5.00 <0.00> (ø)

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