Fix CurlClient & StreamClient on default mode verify_peer and null ca_info

[eclipxe13]

The default mode for CurlClient and StreamClient is to verify peers, chich is good.
This is set in HTTPOptions.

The problem is that CurlClient and StreamClient set the value even if it is NULL and it make it fail instead of using default configured/system default values.

In this PR:
CurlClient (on CurlHandle) only set this option if can evaluate to true
StreamClient only set this option if can evaluate to true.

Feel free if you found a better way to test it or you don't like the way I did it.

[codecov-io]

Codecov Report

Merging #3 into master will decrease coverage by 0.08%.
The diff coverage is 75%.

@@             Coverage Diff             @@
##             master      #3      +/-   ##
===========================================
- Coverage     95.28%   95.2%   -0.09%     
- Complexity      385     386       +1     
===========================================
  Files            28      28              
  Lines          1061    1063       +2     
===========================================
+ Hits           1011    1012       +1     
- Misses           50      51       +1

Impacted Files	Coverage Δ	Complexity Δ
src/Psr18/StreamClient.php	63.63% <100%> (ø)	11 <0> (ø)	⬇️
src/Psr18/CurlHandle.php	78.72% <66.66%> (-0.63%)	35 <0> (+1)

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[codemasher]

See #2 (comment)