[contrib] validate_failures.py: Another fix for GCC's results

Some of GCC's random .json results files cannot even be parsed.
(for instance gotools/check-go-dir/src/cmd/internal/test2json/testdata/ascii.json)

Skip them intead of crashing.

Change-Id: Ib8b0ecfffeef932a3114181c351d3460c558b52a
diff --git a/contrib/testsuite-management/validate_failures.py b/contrib/testsuite-management/validate_failures.py
index c89c613..2efd70f 100755
--- a/contrib/testsuite-management/validate_failures.py
+++ b/contrib/testsuite-management/validate_failures.py
@@ -438,7 +438,15 @@
   json_input = sum_fname.endswith('.json')
 
   if json_input:
-    file_results = json.load(sum_file)
+    try:
+      file_results = json.load(sum_file)
+    except:
+      if _OPTIONS.verbosity >= 2:
+        # GCC's testing generates random .json files, which we can detect
+        # as results.  Some of them cannot even be parsed.
+        print(f'WARNING: cannot parse JSON result file "{sum_fname}"')
+      return result_set
+
     if not 'tests' in file_results:
       if _OPTIONS.verbosity >= 2:
         # GCC's testing generates random .json files, which we can detect