Bug 1610426 - Discard unknown crash annotations r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D60498

--HG--
extra : moz-landing-system : lando

ipc/glue/CrashReporterMetadataShmem.cpp

@@ -207,6 +207,10 @@ void CrashReporterMetadataShmem::ReadAppNotes(const Shmem& aShmem,
           return;
         }
 
+        if (key >= Annotation::Count) {
+          return;
+        }
+
         aNotes[key] = value;
         break;
       }