Use semantic version and prevent crash if version is missing

[chapulina]

I was getting a crash while downloading a model with a malformed config:

$ ign fuel download -j 4 -v 4 -u "https://fuel.ignitionrobotics.org/1.0/openrobotics/models/Universal Robotics UR10 robot arm"
...
terminate called after throwing an instance of 'std::logic_error'                                                                           
  what():  basic_string::_M_construct null not valid                     
Aborted (core dumped)   

The problem is that the <sdf> element of that model doesn't have a version attribute.

To prevent a crash, I'm assuming a version 0.0.1.

Which begs the question, is that version meant to be semantic? I don't think that has been specified anywhere. But considering that most models have a version in the format X.X, I think semantic versioning would make more sense than doubles. That is, 1.12 is larger than 1.2. So I also updated the logic to use Ignition Math's SemanticVersion class. This adds an explicit dependency on ign-math, but that should be ok, because that was already an indirect dependency through ign-common and ign-msgs.

[codecov]

Codecov Report

Merging #151 (bb85340) into ign-fuel-tools4 (21e8b0f) will decrease coverage by 0.06%.
The diff coverage is 62.50%.

@@                 Coverage Diff                 @@
##           ign-fuel-tools4     #151      +/-   ##
===================================================
- Coverage            78.55%   78.48%   -0.07%     
===================================================
  Files                   19       19              
  Lines                 2583     2589       +6     
===================================================
+ Hits                  2029     2032       +3     
- Misses                 554      557       +3     

Impacted Files	Coverage Δ
src/LocalCache.cc	79.58% <62.50%> (-0.54%)	⬇️

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[osrf-triage]

This pull request has been mentioned on Gazebo Community. There might be relevant details there:

https://community.gazebosim.org/t/new-ignition-releases-2022-01-10/1228/1