Dont change shard unless you know (#195)

src/query_router.rs

@@ -335,12 +335,18 @@ impl QueryRouter {
                             // or discard shard selection. If they point to the same shard though,
                             // we can let them through as-is.
                             // This is basically building a database now :)
-                            self.active_shard = self.infer_shard(query);
+                            match self.infer_shard(query) {
+                                Some(shard) => {
+                                    self.active_shard = Some(shard);
                                     debug!("Automatically using shard: {:?}", self.active_shard);
                                 }
 
                                 None => (),
                             };
+                        }
+
+                        None => (),
+                    };
 
                     self.active_role = match self.primary_reads_enabled() {
                         false => Some(Role::Replica), // If primary should not be receiving reads, use a replica.