Display better error message on invalid sarif

Specifically, some third party tools do not include a `results`
block for runs when there is an error. This change adds a more
explicit error message for this situation.

Author: aeisenberg

lib/upload-lib.js

@@ -177,6 +177,9 @@ function getSarifFilePaths(sarifPath: string) {
 export function countResultsInSarif(sarif: string): number {
   let numResults = 0;
   for (const run of JSON.parse(sarif).runs) {
+    if (!Array.isArray(run.results)) {
+      throw new Error("Invalid SARIF. Missing 'results' block in run.");
+    }
     numResults += run.results.length;
   }
   return numResults;