Don't fail check_if_qa_only_spec_changes if changed_files.txt missing

Signed-off-by: Rémy Coutable <remy@rymai.me>

tooling/bin/qa/check_if_qa_only_spec_changes

@@ -6,13 +6,17 @@
 # all the files are end-to-end test spec files.
 
 abort("ERROR: Please specify the file containing the list of changed files and a file where the qa only spec files will be written") if ARGV.size != 2
-file_contents = File.read(ARGV.shift).split(' ')
-
-all_files_are_qa_specs = file_contents.all? { |file_path| file_path =~ %r{^qa\/qa\/specs\/features\/} }
 
+changed_files_path = ARGV.shift
 output_file = ARGV.shift
 
+return unless File.exist?(changed_files_path)
+
+changed_files = File.read(changed_files_path).split(' ')
+
+all_files_are_qa_specs = changed_files.all? { |file_path| file_path =~ %r{^qa\/qa\/specs\/features\/} }
+
 if all_files_are_qa_specs
-  qa_spec_paths_trimmed = file_contents.map { |path| path.sub('qa/', '') }
+  qa_spec_paths_trimmed = changed_files.map { |path| path.sub('qa/', '') }
   File.write(output_file, qa_spec_paths_trimmed.join(' '))
 end