S3 stream wrapper write empty files

[howardlopez]

• Updates the S3 stream wrapper to be able to write empty files for PHP 7+

Fixes #1724

[codecov-io]

Codecov Report

Merging #1744 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #1744      +/-   ##
============================================
+ Coverage     94.23%   94.25%   +0.01%     
- Complexity     2998     3000       +2     
============================================
  Files           178      178              
  Lines          8085     8089       +4     
============================================
+ Hits           7619     7624       +5     
+ Misses          466      465       -1

Impacted Files	Coverage Δ	Complexity Δ
src/S3/StreamWrapper.php	97.45% <100%> (+0.31%)	144 <0> (+2)	⬆️

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