Check rate and value are not invalid (#867)

Co-authored-by: Sergio Rojas <[email protected]>

Author: hisergiorojas

src/opentime/rationalTime.h

@@ -23,6 +23,10 @@ class RationalTime {
     RationalTime& operator= (RationalTime const&) = default;
 
     bool is_invalid_time() const {
+        if(std::isnan(_rate) || std::isnan(_value)) {
+            return true;
+        }
+
         return _rate <= 0;
     }