systemLanguage: do not fail parsing if the env is broken

If we cannot parse the locale in the system environment, we
should not fail to parse the svg file, we should simply ignore
the locales we do not understand. Worse case the conditional
will not match
7 jobs for <span class="ref-name">syslang</span> in 28 minutes and 36 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #225247
fedora test

00:10:24

 
  Lint
manual #225249
allowed to fail manual
clippy
manual #225248
allowed to fail manual
rustfmt
passed #225250
tarball

00:09:51

 
  Cross Distro
passed #225253
debian_i386:testing

00:08:19

failed #225252
debian:testing

00:01:44

failed #225251
fedora:rawhide

00:02:20

 
Name Stage Failure
failed
fedora:rawhide Cross Distro
make[2]: *** [Makefile:1900: /builds/pborelli/librsvg/_build/target/debug/librsvg_internals.a] Segmentation fault (core dumped)
make[1]: Leaving directory '/builds/pborelli/librsvg/_build'
make[1]: *** [Makefile:1412: all-recursive] Error 1
make: *** [Makefile:952: all] Error 2
Uploading artifacts...
WARNING: _build/tests/*.log: no matching files
WARNING: _build/tests/output/: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1
failed
debian:testing Cross Distro
make[2]: *** [Makefile:1901: /builds/pborelli/librsvg/_build/target/debug/librsvg_internals.a] Segmentation fault (core dumped)
make[1]: *** [Makefile:1413: all-recursive] Error 1
make[1]: Leaving directory '/builds/pborelli/librsvg/_build'
make: *** [Makefile:953: all] Error 2
Uploading artifacts...
WARNING: _build/tests/*.log: no matching files
WARNING: _build/tests/output/: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1