Bug 463039 - validate values that get passed to clearWatch. jst aWatchId > count. r/sr=jst

dom/src/geolocation/nsGeolocation.cpp

@@ -648,8 +648,7 @@ NS_IMETHODIMP
 nsGeolocation::ClearWatch(PRInt32 aWatchId)
 {
   PRUint32 count = mWatchingCallbacks.Length();
-
-  if (aWatchId < 0 || count == 0 || aWatchId > count + 1)
+  if (aWatchId < 0 || count == 0 || aWatchId > count)
     return NS_ERROR_FAILURE;
 
   mWatchingCallbacks[aWatchId]->MarkCleared();