Change missing code snippet handling in UI

Also, simplify sarif tests.

extensions/ql-vscode/src/remote-queries/view/FileCodeSnippet.tsx

@@ -188,8 +188,6 @@ const FileCodeSnippet = ({
   messageChildren?: React.ReactNode,
 }) => {
 
-  const code = codeSnippet?.text.split('\n') || [];
-
   const startingLine = codeSnippet?.startLine || 0;
   const endingLine = codeSnippet?.endLine || 0;
 
@@ -198,6 +196,18 @@ const FileCodeSnippet = ({
     startingLine,
     endingLine);
 
+  if (!codeSnippet) {
+    return (
+      <Container>
+        <TitleContainer>
+          <Link href={titleFileUri}>{fileLink.filePath}</Link>
+        </TitleContainer>
+      </Container>
+    );
+  }
+
+  const code = codeSnippet.text.split('\n');
+
   return (
     <Container>
       <TitleContainer>

extensions/ql-vscode/test/pure-tests/sarif-processing.test.ts

@@ -438,7 +438,7 @@ describe('SARIF processing', () => {
       expect(actualCodeSnippet).to.deep.equal(expectedCodeSnippet);
     });
 
-    it('should not return errors for result locations with no contextRegion', () => {
+    it('should use highlightedRegion for result locations with no contextRegion', () => {
       const sarif = buildValidSarifLog();
       sarif.runs![0]!.results![0]!.locations![0]!.physicalLocation!.contextRegion = undefined;
 
@@ -623,8 +623,8 @@ describe('SARIF processing', () => {
     expect(msg.startsWith('Error when processing SARIF result')).to.be.true;
   }
 
-  function expectNoParsingError(result: { errors: string[] | undefined }) {
-    const array = result.errors || [];
+  function expectNoParsingError(result: { errors: string[] }) {
+    const array = result.errors;
     expect(array.length, array.join()).to.equal(0);
   }