Ensure all fields have labels

Never show an empty string in the results view. This fixes #535 (again).

extensions/ql-vscode/src/view/result-table-utils.tsx

@@ -68,12 +68,6 @@ export function renderLocation(
   callback?: () => void
 ): JSX.Element {
 
-  if (loc === undefined) {
-    return <span />;
-  } else if (isStringLoc(loc)) {
-    return <a href={loc}>{loc}</a>;
-  }
-
   // If the label was empty, use a placeholder instead, so the link is still clickable.
   let displayLabel = label;
   if (!label) {
@@ -82,6 +76,12 @@ export function renderLocation(
     displayLabel = `[whitespace: "${label}"]`;
   }
 
+  if (loc === undefined) {
+    return <span>{displayLabel}</span>;
+  } else if (isStringLoc(loc)) {
+    return <a href={loc}>{loc}</a>;
+  }
+
   const resolvableLoc = tryGetResolvableLocation(loc);
   if (resolvableLoc !== undefined) {
     return (