Guard against missing config and surface config parsing errors

lib/erb_lint/cli.rb

@@ -221,7 +221,7 @@ def load_config
     rescue Psych::SyntaxError => e
       failure!("error parsing config: #{e.message}")
     ensure
-      @config.merge!(runner_config_override)
+      @config&.merge!(runner_config_override)
     end
 
     def file_loader

spec/erb_lint/cli_spec.rb

@@ -146,6 +146,17 @@ def run(processed_source)
           expect(subject).to(be(true))
         end
       end
+
+      context "when file has a syntax error" do
+        before { FakeFS::FileSystem.clone(File.join(__dir__, "../fixtures"), "/") }
+
+        let(:args) { ["--config", "invalid-config.yml", "--lint-all"] }
+
+        it { expect { subject }.to(output(/error parsing config:/).to_stderr) }
+        it "is not successful" do
+          expect(subject).to(be(false))
+        end
+      end
     end
 
     context "with custom --cache-dir" do

spec/fixtures/invalid-config.yml

@@ -0,0 +1 @@
+]