GSL/Zproject crash when showing supported targets.

[stephan57160]

There are (at least) 2 ways to show the list of supported targets, from project.xml.

Modify project.xml and include something like :
<target name = "?" />
or
<target name = "not-supported-target" />

In both cases, zproject crashes :

...
gsl/4 M: Generating initial .gitattributes file
gsl/4 M: Generating initial .editorconfig file
gsl/4 M: Valid targets are:
(zproject.gsl 280) Undefined expression

I'm able to fix this and have a list like :

gsl/4 M: Generating initial .gitattributes file
gsl/4 M: Generating initial .editorconfig file
gsl/4 M: Valid targets are:
gsl/4 M:     cucumber        Cucumber integration with cucumber-c
gsl/4 M:     android         Native shared library for Android
gsl/4 M:     autotools       GNU build system
gsl/4 M:     cmake           CMake build system
gsl/4 M:     cygwin          Cygwin build system
gsl/4 M:     debian          packaging for Debian
gsl/4 M:     delphi          Delphi binding
gsl/4 M:     docker          packaging for Docker
gsl/4 M:     gyp             GYP build system (project.gyp)
gsl/4 M:     java            Java JNI binding
gsl/4 M:     java-msvc       MSVC builds for Java JNI binding
gsl/4 M:     jenkins         pipeline CI script for jenkins
gsl/4 M:     mingw32         Mingw32 build system
gsl/4 M:     nodejs          Node.js binding
...

I may raise a PR soon, but I'd like some advise :
I suppose the best option would be to stop processing after this list, right ?
But, I cannot find anything in GSL/ZPROJECT for that.
Is there anything available to stop GSL/ZPROJECT, other than calling a missing function ?

[stephan57160]

This one can be closed, as per PR #1285, then.