Bug 559618. Treat negative max-age values as 0. r=jduell

netwerk/protocol/http/src/nsHttpResponseHead.cpp

@@ -534,7 +534,10 @@ nsHttpResponseHead::GetMaxAgeValue(PRUint32 *result)
     if (!p)
         return NS_ERROR_NOT_AVAILABLE;
 
-    *result = (PRUint32) atoi(p + 8);
+    int maxAgeValue = atoi(p + 8);
+    if (maxAgeValue < 0)
+        maxAgeValue = 0;
+    *result = PRUint32(maxAgeValue);
     return NS_OK;
 }