Don't panic if the duration is negative in try_get_or_insert (#3413)

packages/isrg/src/memory_cache.rs

@@ -55,12 +55,15 @@ impl InMemoryCache {
             let age = elapsed.num_seconds();
             // The cache entry is out of date, so we need to remove it.
             if let Some(invalidate_after) = self.invalidate_after {
-                if elapsed.to_std().unwrap() > invalidate_after {
+                // If we can't convert to a std duration, the duration is negative and hasn't elapsed yet.
+                if let Ok(std_elapsed) = elapsed.to_std() {
+                    if std_elapsed > invalidate_after {
                         tracing::trace!("memory cache out of date");
                         memory_cache.pop(route);
                         return Ok(None);
                     }
                 }
+            }
 
             // We need to reborrow because we may have invalidated the lifetime if the route was removed.
             // We know it wasn't because we returned... but rust doesn't understand that.